Method and device for efficient feedback in wireless communication system that supports multiple antennas

ABSTRACT

The present invention relates to a method for allowing a terminal to transmit CSI for downlink transmission from a base station through an uplink comprises the steps of: receiving a downlink signal through a downlink channel; generating CSI that contains one or more indicators among an RI, a PMI, and CQI for the downlink channel; and transmitting the CSI through an uplink channel, wherein the CSI can contain one or more pieces of information among a first type of CSI which is determined on the basis of a rank N that is determined by the terminal and a second type of CSI which is determined on the basis of a rank that is restricted by a reference value M.

This Application is a 35 U.S.C. §371 National Stage Entry ofInternational Application No. PCT/KR2011/006849 filed Sep. 16, 2011 andclaims the benefit of U.S. Provisional Application Nos. 61/383,348 filedSep. 16, 2010, 61/384,637 filed Sep. 20, 2010, 61/413,951 filed Nov. 15,2010 and Korean Application No. 10-2011-0092504 filed Sep. 14, 2011, allof which are incorporated by reference in their entirety herein.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly to a method and apparatus for performing effectivefeedback in a wireless communication system supporting multipleantennas.

BACKGROUND ART

Generally, Multiple-Input Multiple-Output (MIMO) technology willhereinafter be described in detail. In brief, MIMO is an abbreviationfor Multi-Input Multi-Output. MIMO technology uses multiple transmission(Tx) antennas and multiple reception (Rx) antennas to improve theefficiency of transmission/reception (Tx/Rx), whereas the conventionalart generally uses a single transmission (Tx) antenna and a singlereception (Rx) antenna. In other words, MIMO technology allows atransmitting end and a receiving end to use multiple antennas so as toincrease capacity or improve performance. If necessary, MIMO technologymay also be called multi-antenna technology. In order to correctlyperform multi-antenna transmission, the MIMO system has to receivefeedback information regarding channels from a receiving end designed toreceive multi-antenna channels.

Various feedback information fed back from the receiving end to thetransmitting end in the legacy MIMO wireless communication system may bedefined, for example, a rank indicator (RI), a precoding matrix index(PMI), channel quality information (CQI), etc. Such feedback informationmay be configured as information appropriate for legacy MIMOtransmission.

There is a need for a new system including the extended antennaconfiguration as compared to the legacy MIMO wireless communicationsystem to be developed and introduced to the market. For example,although the legacy system can support a maximum of 4 transmissionantennas, new systems have an extended antenna configuration thatsupports MIMO transmission based on 8 transmission antennas, resultingin increased system capacity.

DISCLOSURE Technical Problem

The new system supporting the extended antenna configuration is designedto perform more complicated MIMO transmission than the legacy MIMOtransmission operation, such that it is impossible to correctly supportthe MIMO operation for the new system only using feedback informationdefined for the legacy MIMO transmission operation.

An object of the present invention is to provide a method and apparatusfor configuring and transmitting feedback information used for correctlyand efficiently supporting MIMO operation based on an extended antennaconfiguration.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

Technical Solution

The object of the present invention can be achieved by providing amethod for transmitting channel state information, CSI, for a downlinktransmission from a base station at a user equipment, UE, through anuplink in a wireless communication system, the method comprising:receiving a downlink signal through a downlink channel; generating theCSI including at least one of a rank indicator, RI, a precoding matrixindicator, PMI, and a channel quality indicator, CQI, for the downlinkchannel; and transmitting the CSI through an uplink channel, wherein theCSI includes at least one of a first type CSI that is determined basedon rank N determined by the UE and a second type CSI that is determinedbased on a rank restricted by a reference value M.

In another aspect of the present invention, a method for receivingchannel state information, CSI, for a downlink transmission at a basestation through an uplink from a user equipment, UE, in a wirelesscommunication system, the method comprising: transmitting a downlinksignal through a downlink channel; and receiving the CSI through anuplink channel, wherein the CSI includes at least one of a rankindicator, RI, a precoding matrix indicator, PMI, and a channel qualityindicator, CQI, for the downlink channel, wherein the CSI includes atleast one of a first type CSI that is determined based on rank Ndetermined by the UE and a second type CSI that is determined based on arank restricted by a reference value M.

In still another aspect of the present invention, a user equipment, UE,for transmitting channel state information, CSI, for a downlinktransmission through an uplink in a wireless communication system, theUE comprising: a receiving module configured to receive a downlinksignal from a base station; a transmitting module configured to transmitan uplink signal to the base station; and a processor configured tocontrol the UE including the receiving module and the transmittingmodule, wherein the processor is further configured to: receive, usingthe receiving module, a downlink signal through a downlink channel;generate the CSI including at least one of a rank indicator, RI, aprecoding matrix indicator, PMI, and a channel quality indicator, CQI,for the downlink channel; and transmit, using the transmitting module,the CSI through an uplink channel, wherein the CSI includes at least oneof a first type CSI that is determined based on rank N determined by theUE and a second type CSI that is determined based on a rank restrictedby a reference value M.

In still another aspect of the present invention, a base station forreceiving channel state information, CSI, for a downlink transmissionthrough an uplink in a wireless communication system, the base stationcomprising: a receiving module configured to receive an uplink signalfrom a user equipment. UE; a transmitting module configured to transmita downlink signal to the UE; and a processor configured to control thebase station including the receiving module and the transmitting module,wherein the processor is further configured to: transmit, using thetransmitting module, a downlink signal through a downlink channel; andreceive, using the receiving module, the CSI through an uplink channel,wherein the CSI includes at least one of a rank indicator, RI, aprecoding matrix indicator, PMI, and a channel quality indicator, CQI,for the downlink channel, wherein the CSI includes at least one of afirst type CSI that is determined based on rank N determined by the UEand a second type CSI that is determined based on a rank restricted by areference value M.

The embodiments of the present invention have the following features.

The CSI includes the first type CSI and the second type CSI if N>M, andthe CSI include the first type CSI if N≦M.

The uplink channel is a physical uplink shared channel, PUSCH, and thefirst type CSI or the second type CSI is transmitted based on downlinkcontrol information, DCI, including a CSI report request field.

The first type CSI is transmitted, if information on scheduling uplinkmultiple transport blocks is included in the DCI or information on thereference value M is not included in the DCI, and the second type CSI istransmitted, if information on scheduling uplink single transport blockis included in the DCI or information on the reference value M isincluded in the DCI.

The first type CSI or the second type CSI is transmitted based onwhether an index of a downlink subframe in which the DCI is received oran index of an uplink subframe in which the CSI is transmitted is 2k+1(where k is a natural number).

The PMI included in the second type CSI is configured as a subset of thePMI included in the first type CSI.

The subset is selected according to a predetermined rule, or informationon a selection of the subset is included in the CSI.

The transmitting the CSI includes transmitting the RI, the PMI and theCQI of the first type CSI, and the CQI of the second type CSI.

The transmitting the CSI further includes transmitting the PMI of thesecond type CSI or a precoder selection indication, PSI.

The uplink channel is a physical uplink control channel, PUCCH, and thesecond type CSI is transmitted instead of the first type CSI in a partof uplink subframes configured for transmitting the first type CSI.

The uplink channel is a physical uplink control channel, PUCCH, and thesecond type CSI is transmitted in an uplink subframe which is after, bya predetermined offset, an uplink subframe in which the first type CSIis transmitted.

A downlink bandwidth represented by the second type CSI is determinedbased on the first type CSI.

The PMI includes a first index and a second index, and the CQI isdetermined by a combination of the first index and the second index.

The above general description of the present invention and a detaileddescription thereof which will be described hereinbelow are exemplaryand are for an additional description of the invention disclosed in theaccompanying claims.

Advantageous Effects

The embodiments of the present invention provide a method and apparatusfor configuring and transmitting feedback information used for correctlyand efficiently supporting MIMO operation based on an extended antennaconfiguration.

The effects of the present invention are not limited to theabove-described effects and other effects which are not described hereinwill become apparent to those skilled in the art from the followingdescription.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 exemplarily shows a radio frame structure for use in a 3rdGeneration Partnership Project Long Term Evolution (3GPP LTE) system;

FIG. 2 exemplarily shows a resource grid of a downlink (DL) slot;

FIG. 3 is a downlink (DL) subframe structure;

FIG. 4 is an uplink (UL) subframe structure;

FIG. 5 shows a physical layer (L1) and a MAC layer (L2) of amulti-carrier supported system;

FIG. 6 is a conceptual diagram illustrating downlink (DL) and uplink(UL) component carriers (CCs);

FIG. 7 shows an exemplary linkage of DL/UL CCs;

FIG. 8 is a conceptual diagram illustrating an SC-FDMA transmissionscheme and an OFDMA transmission scheme;

FIG. 9 is a conceptual diagram illustrating maximum transmission powerfor single antenna transmission and MIMO transmission;

FIG. 10 is a conceptual diagram illustrating a MIMO communicationsystem;

FIG. 11 is a conceptual diagram illustrating a general CDD structure foruse in a MIMO system;

FIG. 12 is a conceptual diagram illustrating codebook-based precoding;

FIG. 13 shows a resource mapping structure of PUCCH;

FIG. 14 shows a channel structure of a CQI information bit;

FIG. 15 is a conceptual diagram illustrating transmission of CQI andACK/NACK information;

FIG. 16 is a conceptual diagram illustrating feedback of channel statusinformation;

FIG. 17 shows an example of a CQI report mode;

FIG. 18 is a conceptual diagram illustrating a method for enabling auser equipment (UE) to periodically transmit channel information;

FIG. 19 is a conceptual diagram illustrating SB CQI transmission;

FIG. 20 is a conceptual diagram illustrating transmission of WB CQI andSB CQI;

FIG. 21 is a conceptual diagram illustrating transmission of WB CQI, SBCQI and RI;

FIGS. 22 and 23 illustrate examples of the restricted rank PMI/CQItransmission timing and offset;

FIGS. 24 to 26 illustrate the restricted rank PMI/CQI reporting cycles;

FIG. 27 illustrates a method for transmitting channel informationaccording to a PUCCH report mode 2-1;

FIG. 28 illustrates a method for transmitting channel informationaccording to a PUCCH report mode 2-1 on the condition that some channelinformation is omitted;

FIG. 29 illustrates an exemplary time point at which channel informationis reported through uplink;

FIG. 30 illustrates an exemplary channel information report time pointfor PUCCH report mode 2-1 depending upon a PTI value;

FIGS. 31 and 32 illustrate a method for transmitting channel informationaccording to a PUCCH report mode 2-1 on the condition that some channelinformation is omitted;

FIG. 33 illustrates WB CQI/WB W2 and SB CQI/SB W2 report cycles;

FIG. 34 illustrates a flow diagram describing a method of transmittingchannel state information according to the present invention;

FIG. 35 illustrates configurations of a base station apparatus and auser equipment apparatus according to the present invention.

BEST MODE

The following embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered to optional factors on thecondition that there is no additional remark. If required, theindividual constituent components or characteristics may not be combinedwith other components or characteristics. Also, some constituentcomponents and/or characteristics may be combined to implement theembodiments of the present invention. The order of operations to bedisclosed in the embodiments of the present invention may be changed.Some components or characteristics of any embodiment may also beincluded in other embodiments, or may be replaced with those of theother embodiments as necessary.

The embodiments of the present invention are disclosed on the basis of adata communication relationship between a base station and a terminal.In this case, the base station is used as a terminal node of a networkvia which the base station can directly communicate with the terminal.Specific operations to be conducted by the base station in the presentinvention may also be conducted by an upper node of the base station asnecessary.

In other words, it will be obvious to those skilled in the art thatvarious operations for enabling the base station to communicate with theterminal in a network composed of several network nodes including thebase station will be conducted by the base station or other networknodes other than the base station. The term “Base Station (BS)” may bereplaced with a fixed station, Node-B, eNode-B (eNB), or an access pointas necessary. The term “relay” may be replaced with a Relay Node (RN) ora Relay Station (RS). The term “terminal” may also be replaced with aUser Equipment (UE), a Mobile Station (MS), a Mobile Subscriber Station(MSS) or a Subscriber Station (SS) as necessary.

It should be noted that specific terms disclosed in the presentinvention are proposed for convenience of description and betterunderstanding of the present invention, and the use of these specificterms may be changed to other formats within the technical scope orspirit of the present invention.

In some instances, well-known structures and devices are omitted inorder to avoid obscuring the concepts of the present invention and theimportant functions of the structures and devices are shown in blockdiagram form. The same reference numbers will be used throughout thedrawings to refer to the same or like parts.

Exemplary embodiments of the present invention are supported by standarddocuments disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802 system, a 3^(rd) Generation Project Partnership (3GPP) system, a3GPP Long Term Evolution (LTE) system, an LTE-Advanced (LTE-A) system,and a 3GPP2 system. In particular, the steps or parts, which are notdescribed to clearly reveal the technical idea of the present invention,in the embodiments of the present invention may be supported by theabove documents. All terminology used herein may be supported by atleast one of the above-mentioned documents.

The following embodiments of the present invention can be applied to avariety of wireless access technologies, for example, CDMA (CodeDivision Multiple Access), FDMA (Frequency Division Multiple Access),TDMA (Time Division Multiple Access), OFDMA (Orthogonal FrequencyDivision Multiple Access), SC-FDMA (Single Carrier Frequency DivisionMultiple Access), and the like. CDMA may be embodied through wireless(or radio) technology such as UTRA (Universal Terrestrial Radio Access)or CDMA2000. TDMA may be embodied through wireless (or radio) technologysuch as GSM (Global System for Mobile communications)/GPRS (GeneralPacket Radio Service)/EDGE (Enhanced Data Rates for GSM Evolution).OFDMA may be embodied through wireless (or radio) technology such asInstitute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi),IEEE 802.16 (WiMAX), IEEE 802-20, and E-UTRA (Evolved UTRA). UTRA is apart of UMTS (Universal Mobile Telecommunications System). 3GPP (3rdGeneration Partnership Project) LTE (long term evolution) is a part ofE-UMTS (Evolved UMTS), which uses E-UTRA. 3GPP LTE employs OFDMA indownlink and employs SC-FDMA in uplink. LTE-Advanced (LTE-A) is anevolved version of 3GPP LTE. WiMAX can be explained by an IEEE 802.16e(WirelessMAN-OFDMA Reference System) and an advanced IEEE 802.16m(WirelessMAN-OFDMA Advanced System). For clarity, the followingdescription focuses on 3GPP LTE and 3GPP LTE-A systems. However,technical features of the present invention are not limited thereto.

FIG. 1 exemplarily shows a radio frame structure for use in a 3rdGeneration Partnership Project Long Term Evolution (3GPP LTE) system. Adownlink (DL) radio frame structure will hereinafter be described withreference to FIG. 1. In a cellular Orthogonal Frequency DivisionMultiplexing (OFDM) radio packet communication system, uplink/downlinkdata packet transmission is performed in subframe units. One subframe isdefined as a predetermined time interval including a plurality of OFDMsymbols. The 3GPP LTE standard supports a type 1 radio frame structureapplicable to Frequency Division Duplexing (FDD) and a type 2 radioframe structure applicable to Time Division Duplexing (TDD).

FIG. 1( a) is a diagram showing the structure of the type 1 radio frame.A downlink radio frame includes 10 subframes, and one subframe includestwo slots in a time region. A time required for transmitting onesubframe is defined in a Transmission Time Interval (TTI). For example,one subframe may have a length of 1 ms and one slot may have a length of0.5 ms. One slot may include a plurality of OFDM symbols in a timeregion and include a plurality of Resource Blocks (RBs) in a frequencydomain. Since the 3GPP LTE system uses OFDMA in downlink, the OFDMsymbol indicates one symbol duration. The OFDM symbol may be called anSC-FDMA symbol or a symbol duration. RB is a resource allocation unitand includes a plurality of contiguous carriers in one slot.

The number of OFDM symbols included in one slot may be changed accordingto the configuration of a Cyclic Prefix (CP). The CP includes anextended CP and a normal CP. For example, if the OFDM symbols areconfigured by the normal CP, the number of OFDM symbols included in oneslot may be seven. If the OFDM symbols are configured by the extendedCP, the length of one OFDM symbol is increased, the number of OFDMsymbols included in one slot is less than that of the case of the normalCP. In case of the extended CP, for example, the number of OFDM symbolsincluded in one slot may be six. If the channel state is unstable, forexample, if a User Equipment (UE) moves at a high speed, the extended CPmay be used in order to further reduce interference between symbols.

In case of using the normal CP, since one slot includes seven OFDMsymbols, one subframe includes 14 OFDM symbols. At this time, the firsttwo or three OFDM symbols of each subframe may be allocated to aPhysical Downlink Control Channel (PDCCH) and the remaining OFDM symbolsmay be allocated to a Physical Downlink Shared Channel (PDSCH).

The structure of a type 2 radio frame is shown in FIG. 1( b). The type 2radio frame includes two half-frames, each of which is made up of fivesubframes, a downlink pilot time slot (DwPTS), a guard period (GP), andan uplink pilot time slot (UpPTS), in which one subframe consists of twoslots. That is, one subframe is composed of two slots irrespective ofthe radio frame type. DwPTS is used to perform initial cell search,synchronization, or channel estimation. UpPTS is used to perform channelestimation of a base station and uplink transmission synchronization ofa user equipment (UE). The guard interval (GP) is located between anuplink and a downlink so as to remove interference generated in theuplink due to multi-path delay of a downlink signal. That is, onesubframe is composed of two slots irrespective of the radio frame type.

The structure of the radio frame is only exemplary. Accordingly, thenumber of subframes included in the radio frame, the number of slotsincluded in the subframe or the number of symbols included in the slotmay be changed in various manners.

FIG. 2 is a diagram showing a resource grid in a downlink slot. Althoughone downlink slot includes seven OFDM symbols in a time domain and oneRB includes 12 subcarriers in a frequency domain in the figure, thescope or spirit of the present invention is not limited thereto. Forexample, in case of a normal Cyclic Prefix (CP), one slot includes 7OFDM symbols. However, in case of an extended CP, one slot may include 6OFDM symbols. Each element on the resource grid is referred to as aresource element. One RB includes 12×7 resource elements. The numberN^(DL) of RBs included in the downlink slot is determined based ondownlink transmission bandwidth. The structure of the uplink slot may beequal to the structure of the downlink slot.

FIG. 3 is a diagram showing the structure of a downlink subframe. Amaximum of three OFDM symbols of a front portion of a first slot withinone subframe corresponds to a control region to which a control channelis allocated. The remaining OFDM symbols correspond to a data region towhich a Physical Downlink Shared Channel (PDSCH) is allocated. The basicunit of transmission becomes one subframe. Examples of the downlinkcontrol channels used in the 3GPP LTE system include, for example, aPhysical Control Format Indicator Channel (PCFICH), a Physical DownlinkControl Channel (PDCCH), a Physical Hybrid automatic repeat requestIndicator Channel (PHICH), etc. The PCFICH is transmitted at a firstOFDM symbol of a subframe, and includes information about the number ofOFDM symbols used to transmit the control channel in the subframe. ThePHICH includes a HARQ ACK/NACK signal as a response to uplinktransmission. The control information transmitted through the PDCCH isreferred to as Downlink Control Information (DCI). The DCI includesuplink or downlink scheduling information or an uplink transmit powercontrol command for a certain UE group. The PDCCH may include resourceallocation and transmission format of a Downlink Shared Channel(DL-SCH), resource allocation information of an Uplink Shared Channel(UL-SCH), paging information of a Paging Channel (PCH), systeminformation on the DL-SCH, resource allocation of a higher layer controlmessage such as a Random Access Response (RAR) transmitted on the PDSCH,a set of transmit power control commands for individual UEs in a certainUE group, transmit power control information, activation of Voice overIP (VoIP), etc. A plurality of PDCCHs may be transmitted within thecontrol region. The UE may monitor the plurality of PDCCHs. The PDCCHsare transmitted on an aggregation of one or several contiguous controlchannel elements (CCEs). The CCE is a logical allocation unit used toprovide the PDCCHs at a coding rate based on the state of a radiochannel. The CCE corresponds to a plurality of resource element groups.The format of the PDCCH and the number of available bits are determinedbased on a correlation between the number of CCEs and the coding rateprovided by the CCEs. The base station determines a PDCCH formataccording to a DCI to be transmitted to the UE, and attaches a CyclicRedundancy Check (CRC) to control information. The CRC is masked with aRadio Network Temporary Identifier (RNTI) according to an owner or usageof the PDCCH. If the PDCCH is for a specific UE, a cell-RNTI (C-RNTI) ofthe UE may be masked to the CRC. Alternatively, if the PDCCH is for apaging message, a paging indicator identifier P-RNTI) may be masked tothe CRC. If the PDCCH is for system information (more specifically, asystem information block (SIB)), a system information identifier and asystem information RNTI (SI-RNTI) may be masked to the CRC. To indicatea random access response that is a response for transmission of a randomaccess preamble of the UE, a random access-RNTI (RA-RNTI) may be maskedto the CRC.

FIG. 4 is a diagram showing the structure of an uplink frame. The uplinksubframe may be divided into a control region and a data region in afrequency region. A Physical Uplink Control Channel (PUCCH) includinguplink control information is allocated to the control region. APhysical uplink Shared Channel (PUSCH) including user data is allocatedto the data region. In order to maintain single carrier characteristics,one UE does not simultaneously transmit the PUCCH and the PUSCH. ThePUCCH for one UE is allocated to an RB pair in a subframe. RBs belongingto the RB pair occupy different subcarriers with respect to two slots.Thus, the RB pair allocated to the PUCCH is “frequency-hopped” at a slotedge.

Carrier Aggregation

Although downlink and uplink bandwidths are different from each other, awireless communication system typically uses one carrier. For example, awireless communication system having one carrier for each of thedownlink and the uplink and symmetry between the downlink and uplinkbandwidths may be provided based on a single carrier.

The International Telecommunication Union (ITU) requests thatIMT-Advanced candidates support wider bandwidths, compared to legacywireless communication systems. However, allocation of a wide frequencybandwidth is difficult throughout most of the world. Accordingly, atechnology for efficiently using small segmented bands, known as carrieraggregation (bandwidth aggregation) or spectrum aggregation, has beendeveloped in order to aggregate a plurality of physical bands to a widerlogical band.

Carrier aggregation was introduced to support increased throughput,prevent cost increase caused by introduction of wideband RF devices, andensure compatibility with legacy systems. Carrier aggregation enablesdata exchange between a UE and an eNB through a group of carriers eachhaving a bandwidth unit defined in a legacy wireless communicationsystem (e.g. 3GPP LTE Release-8 or Release-9 in case of 3GPP LTE-A). Thecarriers each having a bandwidth unit defined in the legacy wirelesscommunication system may be called Component Carriers (CCs). Carrieraggregation using one or more CCs may be applied to each of downlink anduplink. Carrier aggregation may support a system bandwidth of up to 100MHz by aggregating up to five CCs each having a bandwidth of 5, 10 or 20MHz.

A downlink CC and an uplink CC may be represented as a DL CC and a ULCC, respectively. A carrier or CC may be represented as a cell in termsof function in the 3GPP LTE system. Thus, a DL CC and a UL CC may bereferred to as a DL cell and a UL cell, respectively. Hereinbelow, theterms ‘carriers’, ‘component carriers’, ‘CCs’ or ‘cells’ will be used tosignify a plurality of carriers to which carrier aggregation is applied.

While the following description exemplarily uses an eNB (BS) or cell asa downlink transmission entity and exemplarily uses a UE as an uplinktransmission entity, the scope or spirit of the present invention is notlimited thereto. That is, even when a relay node (RN) may be used as adownlink transmission entity from an eNB to a UE and or be used as anuplink reception entity from a UE to an eNB, or even when the RN may beused an uplink transmission entity for a UE or be used as a downlinkreception entity from an eNB, it should be noted that the embodiments ofthe present invention can be applied without difficulty.

Downlink carrier aggregation may be described as an eNB supportingdownlink transmission to a UE in frequency resources (subcarriers orphysical resource blocks [PRBs]) of one or more carrier bands in timeresources (allocated in units of a subframe). Uplink carrier aggregationmay be described as a UE supporting uplink transmission to an eNB infrequency resources (subcarriers or PRBs) of one or more carrier bandsin time resources (allocated in units of a subframe).

FIG. 5 shows a physical layer (first layer, L1) and a MAC layer (secondlayer, L2) of a multi-carrier supported system. Referring to FIG. 5, aneNB or BS of the legacy wireless communication system supporting asingle carrier includes one physical layer (PHY) entity capable ofsupporting one carrier, and one medium access control (MAC) entity forcontrolling one PHY entity may be provided to the eNB. For example,baseband processing may be carried out in the PHY layer. For example,the L1/L2 scheduler operation including not only MAC PDU (Protocol DataUnit) creation of a transmitter but also MAC/RLC sub-layers may becarried out in the MAC layer. The MAC PDU packet block of the MAC layeris converted into a transport block through a logical transport layer,such that the resultant transport block is mapped to a physical layerinput information block. In FIG. 5, the MAC layer is represented as theentire L2 layer, and may conceptually cover MAC/RLC/PDCP sub-layers. Forconvenience of description and better understanding of the presentinvention, the above-mentioned application may be used interchangeablyin the MAC layer description of the present invention.

On the other hand, a multicarrier-supporting system may provide aplurality of MAC-PHY entities. In more detail, as can be seen from FIG.5( a), the transmitter and receiver of the multicarrier-supportingsystem may be configured in such a manner that one MAC-PHY entity ismapped to each of n component carriers (n CCs). An independent PHY layerand an independent MAC layer are assigned to each CC, such that a PDSCHfor each CC may be created in the range from the MAC PDU to the PHYlayer.

Alternatively, the multicarrier-supporting system may provide one commonMAC entity and a plurality of PHY entities. That is, as shown in FIG. 5(b), the multicarrier-supporting system may include the transmitter andthe receiver in such a manner that n PHY entities respectivelycorrespond to n CCs and one common MAC entity controlling the n PHYentities may be present in each of the transmitter and the receiver. Inthis case, a MAC PDU from one MAC layer may be branched into a pluralityof transport blocks corresponding to a plurality of CCs through atransport layer. Alternatively, when generating a MAC PDU in the MAClayer or when generating an RLC PDU in the RLC layer, the MAC PDU or RLCPDU may be branched into individual CCs. As a result, a PDSCH for eachCC may be generated in the PHY layer.

PDCCH for transmitting L1/L2 control signaling control informationgenerated from a packet scheduler of the MAC layer may be mapped tophysical resources for each CC, and then transmitted. In this case,PDCCH that includes control information (DL assignment or UL grant) fortransmitting PDSCH or PUSCH to a specific UE may be separately encodedat every CC to which the corresponding PDSCH/PUSCH is transmitted. ThePDCCH may be called a separate coded PDCCH. On the other hand,PDSCH/PUSCH transmission control information of several CCs may beconfigured in one PDCCH such that the configured PDCCH may betransmitted. This PDCCH may be called a joint coded PDCCH.

To support carrier aggregation, connection between a BS (or eNB) and aUE (or RN) needs to be established and preparation of connection setupbetween the BS and the UE is needed in such a manner that a controlchannel (PDCCH or PUCCH) and/or a shared channel (PDSCH or PUSCH) can betransmitted. In order to perform the above-mentioned connection orconnection setup for a specific UE or RN, measurement and/or reportingfor each carrier are needed, and CCs serving as the measurement and/orreporting targets may be assigned. In other words, CC assignment meansthat CCs (indicating the number of CCs and indexes of CCs) used forDL/UL transmission are established in consideration of not onlycapabilities of a specific UE (or RN) from among UL/DL CCs constructedin the BS but also system environment.

In this case, when CC assignment is controlled in third layer (L3) RadioResource Management (RRM), UE-specific or RN-specific RRC signaling maybe used. Alternatively, cell-specific or cell cluster-specific RRCsignaling may be used. Provided that dynamic control such as a series ofCC activation/deactivation settings is needed for CC assignment, apredetermined PDCCH may be used for L1/L2 control signaling, or adedicated physical control channel for CC assignment control informationor an L2 MAC-message formatted PDSCH may be used. On the other hand, ifCC assignment is controlled by a packet scheduler, a predetermined PDCCHmay be used for L1/L2 control signaling, a physical control channeldedicated for CC assignment control information may be used, or a PDSCHconfigured in the form of an L2 MAC message may be used.

FIG. 6 is a conceptual diagram illustrating downlink (DL) and uplink(UL) component carriers (CCs). Referring to FIG. 6, DL and UL CCs may beassigned from an eNB (cell) or RN. For example, the number of DL CCs maybe set to N and the number of UL CCs may be set to M.

Through the UE's initial access or initial deployment process, after RRCconnection is established on the basis of one certain CC for DL or UL(cell search) (for example, system information acquisition/reception,initial random access process, etc.), a unique carrier setup for each UEmay be provided from a dedicated signaling (UE-specific RRC signaling orUE-specific L1/L2 PDCCH signaling). For example, assuming that a carriersetup for UE is commonly achieved in units of an eNB (cell orcell-cluster), the UE carrier setup may also be provided throughcell-specific RRC signaling or cell-specific UE-common L1/L2 PDCCHsignaling. In another example, carrier component information for use inan eNB may be signaled to a UE through system information for RRCconnection setup, or may also be signaled to additional systeminformation or cell-specific RRC signaling upon completion of the RRCconnection setup.

While DL/UL CC setup has been described, centering on the relationshipbetween an eNB and a UE, to which the present invention is not limited,an RN may also provide DL/UL CC setup to a UE contained in an RN region.In addition, in association with an RN contained in an eNB region, theeNB may also provide DL/UL CC setup of the corresponding RN to the RN ofthe eNB region. For clarity, while the following description willdisclose DL/UL CC setup on the basis of the relationship between the eNBand the UE, it should be noted that the same content may also be appliedto the relationship between the RN and the UE (i.e., access uplink anddownlink) or the relation between the eNB and the RN (backhaul uplink ordownlink) without departing from the scope or spirit of the presentinvention.

When the above-mentioned DL/UL CCs are uniquely assigned to individualUEs, DL/UL CC linkage may be implicitly or explicitly configured througha certain signaling parameter definition.

FIG. 7 shows an exemplary linkage of DL/UL CCs. In more detail, when aneNB configures two DL CCs (DL CC #a and DL CC #b) and two UL CCs (UL CC#i and UL CC #j), FIG. 6 shows a DL/UL CC linkage defined when two DLCCs (DL CC #a and DL CC #b) and one UL CC (UL CC #i) are assigned to acertain UE.

In a DL/UL CC linkage setup shown in FIG. 7, a solid line indicates alinkage setup between DL CC and UL CC that are basically constructed byan eNB, and this linkage setup between DL CC and UL CC may be defined in“System Information Block (SIB) 2”. In the DL/UL CC linkage setup shownin FIG. 7, a dotted line indicates a linkage setup between DL CC and ULCC configured in a specific UE. The above-mentioned DL CC and UL CClinkage setup shown in FIG. 7 is disclosed only for illustrativepurposes, and the scope or spirit of the present invention is notlimited thereto. That is, in accordance with various embodiments of thepresent invention, the number of DL CCs or UL CCs configured by an eNBmay be set to an arbitrary number. Thus, the number of UE-specific DLCCs or the number of UE-specific UL CCs in the above-mentioned DL CCs orUL CCs may be set to an arbitrary number, and associated DL/UL CClinkage may be defined in a different way from that of FIG. 7.

Further, from among DL CCs and UL CCs configured or assigned, a primaryCC (PCC), or a primary cell (P-cell) or an anchor CC (also called ananchor cell) may be configured. For example, a DL PCC (or DL P-cell)aiming to transmit configuration/reconfiguration information on RRCconnection setup may be configured. In another example, UL CC fortransmitting PUCCH to be used when a certain UE transmits UCI that mustbe transmitted on uplink may be configured as UL PCC (or UL P-cell). Forconvenience of description, it is assumed that one DL PCC (P-cell) andone UL PCC (P-cell) are basically assigned to each UE. Alternatively, ifa large number of CCs is assigned to UE or if CCs can be assigned from aplurality of eNBs, one or more DL PCCs (P-cells) and/or one or more ULPCCs (P-cells) may be assigned from one or more eNBs to a certain UE.For linkage between DL PCC (P-cell) and UL PCC (P-cell), a UE-specificconfiguration method may be considered by the eNB as necessary. Toimplement a more simplified method, a linkage between DL PCC (P-cell)and UL PCC (P-cell) may be configured on the basis of the relationshipof basic linkage that has been defined in LTE Release-8 (LTE Rel-8) andsignaled to System Information Block (or Base) 2. DL PCC (P-cell) and ULPCC (P-cell) for the above-mentioned linkage configuration are groupedso that the grouped result may be denoted by a UE-specific P-cell.

SC-FDMA Transmission and OFDMA Transmission

FIG. 8 is a conceptual diagram illustrating an SC-FDMA transmissionscheme and an OFDMA transmission scheme for use in a mobilecommunication system. The SC-FDMA transmission scheme may be used for ULtransmission and the OFDMA transmission scheme may be used for DLtransmission.

Each of the UL signal transmission entity (e.g., UE) and the DL signaltransmission entity (e.g., eNB) may include a Serial-to-Parallel (S/P)Converter 801, a subcarrier mapper 803, an M-point Inverse DiscreteFourier Transform (IDFT) module 804, and a Parallel-to-Serial Converter805. Each input signal that is input to the S/P converter 801 may be achannel coded and modulated data symbol. However, a user equipment (UE)for transmitting signals according to the SC-FDMA scheme may furtherinclude an N-point Discrete Fourier Transform (DFT) module 802. Theinfluence of IDFT processing of the M-point IDFT module 804 isconsiderably offset, such that a transmission signal may be designed tohave a single carrier property. That is, the DFT module 802 performs DFTspreading of an input data symbol such that a single carrier propertyrequisite for UL transmission may be satisfied. The SC-FDMA transmissionscheme basically provides good or superior Peak to Average Power ratio(PAPR) or Cubic Metric (CM), such that the UL transmitter can moreeffectively transmit data or information even in the case of the powerlimitation situation, resulting in an increase in user throughput.

FIG. 9 is a conceptual diagram illustrating maximum transmission powerfor single antenna transmission and MIMO transmission. FIG. 9( a) showsthe case of single antenna transmission. As can be seen from FIG. 9( a),one power amplifier (PA) may be provided to one antenna. In FIG. 9( a),an output signal (P_(max)) of the power amplifier (PA) may have aspecific value, for example, 23 dBm. In contrast, FIGS. 9( b) and 9(c)show the case of MIMO transmission. As can be seen from FIGS. 9( b) and9(c), several PAs may be mapped to respective transmission (Tx)antennas. For example, provided that the number of transmission (Tx)antennas is set to 2, 2 PAs may be mapped to respective transmission(Tx) antennas. The setting of output values (i.e., maximum transmissionpower) of 2 PAs may be configured in different ways as shown in FIGS. 9(b) and 9(c).

In FIG. 9( b), maximum transmission power (P_(max)) for single antennatransmission may be divisionally applied to PA1 and PA2. That is, if atransmission power value of x [dBm] is assigned to PA1, a transmissionpower value of (P_(max)−x) [dBm] may be applied to PA2. In this case,since total transmission power (P_(max)) is maintained, the transmittermay have higher robustness against the increasing PAPR in the powerlimitation situation.

On the other hand, as can be seen from FIG. 9( c), only one Tx antenna(ANT1) may have a maximum transmission power value (P_(max)), and theother Tx antenna (ANT2) may have a half value (P_(max)/2) of the maximumtransmission power value (P_(max)). In this case, only one transmissionantenna may have higher robustness against increasing PAPR.

MIMO System

MIMO technology is not dependent on one antenna path to receive onemessage, collects a plurality of data pieces received via severalantennas, and completes total data. As a result, MIMO technology canincrease a data transfer rate within a specific range, or can increase asystem range at a specific data transfer rate. Under this situation,MIMO technology is a next-generation mobile communication technologycapable of being widely applied to mobile communication terminals orRNs. MIMO technology can extend the range of data communication, so thatit can overcome the limited amount of transmission (Tx) data of mobilecommunication systems reaching a critical situation.

FIG. 10( a) is a block diagram illustrating a general MIMO communicationsystem. Referring to FIG. 10( a), if the number of transmission (Tx)antennas increases to N_(t), and at the same time the number ofreception (Rx) antennas increases to N_(R), a theoretical channeltransmission capacity of the MIMO communication system increases inproportion to the number of antennas, differently from theabove-mentioned case in which only a transmitter or receiver usesseveral antennas, so that transfer rate and frequency efficiency can begreatly increased. In this case, the transfer rate acquired by theincreasing channel transmission capacity can theoretically increase by apredetermined amount that corresponds to multiplication of a maximumtransfer rate (R_(o)) acquired when one antenna is used and a rate ofincrease (R_(i)). The rate of increase (R_(i)) can be represented by thefollowing equation 1.R _(i)=min(N _(T) ,N _(R))  [Equation 1]

For example, provided that a MIMO system uses four transmission (Tx)antennas and four reception (Rx) antennas, the MIMO system cantheoretically acquire a high transfer rate which is four times higherthan that of a one antenna system. After the above-mentioned theoreticalcapacity increase of the MIMO system was demonstrated in the mid-1990s,many developers began to conduct intensive research into a variety oftechnologies which can substantially increase data transfer rate usingthe theoretical capacity increase. Some of the above technologies havebeen reflected in a variety of wireless communication standards, forexample, third-generation mobile communication or next-generationwireless LAN, etc.

A variety of MIMO-associated technologies have been intensivelyresearched by many companies or developers, for example, research intoinformation theory associated with MIMO communication capacity undervarious channel environments or multiple access environments, researchinto a radio frequency (RF) channel measurement and modeling of the MIMOsystem, and research into a space-time signal processing technology.

Mathematical modeling of a communication method for use in theabove-mentioned MIMO system will hereinafter be described in detail. Ascan be seen from FIG. 10( a), it is assumed that there are N_(T)transmission (Tx) antennas and N_(R) reception (Rx) antennas. In thecase of a transmission (Tx) signal, a maximum number of transmissioninformation pieces is N_(T) under the condition that N_(T) transmission(Tx) antennas are used, so that the transmission (Tx) information can berepresented by a specific vector shown in the following equation 2.s=└s ₁ ,s ₂ , . . . ,s _(N) _(T) ┘^(T)  [Equation 2]

In the meantime, individual transmission (Tx) information pieces (s₁,s₂, . . . , S_(NT)) may have different transmission powers. In thiscase, if the individual transmission powers are denoted by (P₁, P₂, . .. , P_(NT)), transmission (Tx) information having an adjustedtransmission power can be represented by a specific vector shown in thefollowing equation 3.ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P_(N) _(T) s _(N) _(T) ]^(T)  [Equation 3]

In Equation 3, Ŝ is a transmission vector, and can be represented by thefollowing equation 4 using a diagonal matrix P of a transmission (Tx)power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{t}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In the meantime, the information vector Ŝ having an adjustedtransmission power is applied to a weight matrix (W), so that N_(T)transmission (Tx) signals (x₁, x₂, . . . , x_(NT)) to be actuallytransmitted are configured. In this case, the weight matrix (W) isadapted to properly distribute transmission (Tx) information toindividual antennas according to transmission channel situations. Theabove-mentioned transmission (Tx) signals (x₁, x₂, . . . , x_(NT)) canbe represented by the following equation 5 using the vector (X).

$\begin{matrix}{x = {\quad{\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1\; N_{T}} \\w_{21} & w_{22} & \ldots & w_{2\; N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\hat{s}} = {WPs}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Next, if N_(R) reception (Rx) antennas are used, reception (Rx) signals(y₁, y₂, . . . , y_(NR)) of individual antennas can be represented by aspecific vector (y) shown in the following equation 6.y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Equation 6]

In the meantime, if a channel modeling is executed in the MIMOcommunication system, individual channels can be distinguished from eachother according to transmission/reception (Tx/Rx) antenna indexes. Aspecific channel passing the range from a transmission (Tx) antenna (j)to a reception (Rx) antenna (i) is denoted by h_(u). In this case, itshould be noted that the index order of the channel h_(ij) is locatedbefore a reception (Rx) antenna index and is located after atransmission (Tx) antenna index.

Several channels are tied up, so that they are displayed in the form ofa vector or matrix. An exemplary vector is as follows. FIG. 10( b) showschannels from N_(T) transmission (Tx) antennas to a reception (Rx)antenna (i).

Referring to FIG. 10( b), the channels passing the range from the N_(T)transmission (Tx) antennas to the reception (Rx) antenna (i) can berepresented by the following equation 7.h ₁ ^(T) =└h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ┘  [Equation 7]

If all channels passing the range from the N_(T) transmission (Tx)antennas to N_(R) reception (Rx) antennas are denoted by the matrixshown in Equation 7, the following equation 8 is acquired.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1\; N_{T}} \\h_{21} & h_{22} & \ldots & h_{2\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Additive white Gaussian noise (AWGN) is added to an actual channel whichhas passed the channel matrix (H) shown in Equation 8. The AWGN (n₁, n₂,. . . , n_(NR)) added to each of N_(R) reception (Rx) antennas can berepresented by a specific vector shown in the following equation 9.n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Equation 9]

A reception signal calculated by the above-mentioned equations can berepresented by the following equation 10.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1\; N_{T}} \\h_{21} & h_{22} & \ldots & h_{2\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}{\quad{\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} + {\quad{\begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix} = {{Hx} + n}}}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

In the meantime, the number of rows and the number of columns of achannel matrix H indicating a channel condition are determined by thenumber of Tx/Rx antennas. In the channel matrix H, the number of rows isequal to the number (N_(R)) of Rx antennas, and the number of columns isequal to the number (N_(T)) of Tx antennas. Namely, the channel matrix His denoted by an N_(R)×N_(T) matrix. Generally, a matrix rank is definedby a smaller number between the number of rows and the number ofcolumns, in which the rows and the columns are independent of eachother. Therefore, the matrix rank cannot be higher than the number ofrows or columns. The rank of the channel matrix H can be represented bythe following equation 11.rank(H)≦min(N _(T) ,N _(R))  [Equation 11]

A variety of MIMO transmission/reception (Tx/Rx) schemes may be used foroperating the MIMO system, for example, frequency switched transmitdiversity (FSTD), Space Frequency Block Coding (SFBC), Space Time BlockCoding (STBC), Cyclic Delay Diversity (CDD), time switched transmitdiversity (TSTD), etc. In case of Rank 2 or higher, Spatial Multiplexing(SM), Generalized Cyclic Delay Diversity (GCDD), Selective VirtualAntenna Permutation (S-VAP), etc. may be used.

The FSTD scheme serves to allocate subcarriers having differentfrequencies to signals transmitted through multiple antennas so as toobtain diversity gain. The SFBC scheme efficiently applies selectivityof a spatial region and a frequency region so as to obtain diversitygain and multiuser scheduling gain. The STBC scheme applies selectivityof a spatial domain and a time region. The CDD scheme serves to obtaindiversity gain using path delay between transmission antennas. The TSTDscheme serves to temporally divide signals transmitted through multipleantennas. The spatial multiplexing scheme serves to transmit differentdata through different antennas so as to increase a transfer rate. TheGCDD scheme serves to apply selectivity of a time region and a frequencyregion. The S-VAP scheme uses a single precoding matrix and includes aMulti Codeword (MCW) S-VAP for mixing multiple codewords among antennasin spatial diversity or spatial multiplexing and a Single Codeword (SCW)S-VAP using a single codeword.

In case of the STBC scheme from among the above-mentioned MIMOtransmission schemes, the same data symbol is repeated to supportorthogonality in a time domain so that time diversity can be obtained.Similarly, the SFBC scheme enables the same data symbol to be repeatedto support orthogonality in a frequency domain so that frequencydiversity can be obtained. An exemplary time block code used for STBCand an exemplary frequency block code used for SFBC are shown inEquation 12 and Equation 13, respectively. Equation 12 shows a blockcode of the case of 2 transmission (Tx) antennas, and Equation 13 showsa block code of the case of 4 transmission (Tx) antennas.

$\begin{matrix}{\frac{1}{\sqrt{2}}\begin{pmatrix}S_{1} & S_{2} \\{- S_{2}^{*}} & S_{1}^{*}\end{pmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack \\{\frac{1}{\sqrt{2}}\begin{pmatrix}S_{1} & S_{2} & 0 & 0 \\0 & 0 & S_{3} & S_{4} \\{- S_{2}^{*}} & S_{1}^{*} & 0 & 0 \\0 & 0 & {- S_{4}^{*}} & S_{3}^{*}\end{pmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

In Equations 12 and 13, S_(i) (i=1, 2, 3, 4) means a modulated datasymbol. In addition, each row of the matrixes of Equation 12 and 13 mayindicate an antenna port, and each column may indicate time (in case ofSTBC) or frequency (in case of SFBC).

On the other hand, the CDD scheme from among the above-mentioned MIMOtransmission schemes mandatorily increases delay spread so as toincrease frequency diversity. FIG. 11 is a conceptual diagramillustrating a general CDD structure for use in the MIMO system. FIG.11( a) shows a method for applying cyclic delay to a time domain. Ifnecessary, the CDD scheme based on the cyclic delay of FIG. 11( a) mayalso be implemented as phase-shift diversity of FIG. 11( b).

In association with the above-mentioned MIMO transmission techniques,the codebook-based precoding method will hereinafter be described withreference to FIG. 12. FIG. 12 is a conceptual diagram illustratingcodebook-based precoding.

In accordance with the codebook-based precoding scheme, a transceivermay share codebook information including a predetermined number ofprecoding matrixes according to a transmission rank, the number ofantennas, etc. That is, if feedback information is infinite, theprecoding-based codebook scheme may be used. The receiver measures achannel status through a reception signal, so that an infinite number ofpreferred precoding matrix information (i.e., an index of thecorresponding precoding matrix) may be fed back to the transmitter onthe basis of the above-mentioned codebook information. For example, thereceiver may select an optimum precoding matrix by measuring an ML(Maximum Likelihood) or MMSE (Minimum Mean Square Error) scheme.Although the receiver shown in FIG. 12 transmits precoding matrixinformation for each codeword to the transmitter, the scope or spirit ofthe present invention is not limited thereto.

Upon receiving feedback information from the receiver, the transmittermay select a specific precoding matrix from a codebook on the basis ofthe received information. The transmitter that has selected theprecoding matrix performs a precoding operation by multiplying theselected precoding matrix by as many layer signals as the number oftransmission ranks, and may transmit each precoded Tx signal over aplurality of antennas. If the receiver receives the precoded signal fromthe transmitter as an input, it performs inverse processing of theprecoding having been conducted in the transmitter so that it canrecover the reception (Rx) signal. Generally, the precoding matrixsatisfies a unitary matrix (U) such as (U*U^(H)=I), so that the inverseprocessing of the above-mentioned precoding may be conducted bymultiplying a Hermit matrix (P^(H)) of the precoding matrix H used inthe precoding of the transmitter by the reception (Rx) signal.

Physical Uplink Control Channel (PUCCH)

PUCCH including UL control information will hereinafter be described indetail.

A plurality of UE control information pieces may be transmitted througha PUCCH. When Code Division Multiplexing (CDM) is performed in order todiscriminate signals of UEs, a Constant Amplitude Zero Autocorrelation(CAZAC) sequence having a length of 12 is mainly used. Since the CAZACsequence has a property that a constant amplitude is maintained in atime domain and a frequency domain, a Peak-to-Average Power Ratio (PAPR)of a UE or Cubic Metic (CM) may be decreased to increase coverage. Inaddition, ACK/NACK information for DL data transmitted through the PUCCHmay be covered using an orthogonal sequence.

In addition, control information transmitted through the PUCCH may bediscriminated using cyclically shifted sequences having different cyclicshift values. A cyclically shifted sequence may be generated bycyclically shifting a basic sequence (also called a base sequence) by aspecific cyclic shift (CS) amount. The specific CS amount is indicatedby a CS index. The number of available CS s may be changed according tochannel delay spread. Various sequences may be used as the basicsequence and examples thereof include the above-described CAZACsequence.

PUCCH may include a variety of control information, for example, aScheduling Request (SR), DL channel measurement information, andACK/NACK information for DL data transmission. The channel measurementinformation may include a Channel Quality Indicator (CQI), a PrecodingMatrix Index (PMI), and a Rank Indicator (RI).

PUCCH format may be defined according to the type of control informationcontained in a PUCCH, modulation scheme information thereof, etc. Thatis, PUCCH format 1 may be used for SR transmission, PUCCH format 1a or1b may be used for HARQ ACK/NACK transmission, PUCCH format 2 may beused for CQI transmission, and PUCCH format 2a/2b may be used for HARQACK/NACK transmission.

If HARQ ACK/NACK is transmitted alone in an arbitrary subframe, PUCCHformat 1a or 1b may be used. If SR is transmitted alone, PUCCH format 1may be used. The UE may transmit the HARQ ACK/NACK and the SR throughthe same subframe, and a detailed description thereof will hereinafterbe described in detail.

PUCCH format may be summarized as shown in Table 1.

TABLE 1 Number of PUCCH Modulation bits per format scheme subframe Usageetc. 1 N/A N/A SR (Scheduling Request) 1a BPSK 1 ACK/NACK One codeword1b QPSK 2 ACK/NACK Two codeword 2 QPSK 20 CQI Joint Coding ACK/NACK(extended CP) 2a QPSK + BPSK 21 CQI + ACK/ Normal CP only NACK 2b QPSK +BPSK 22 CQI + ACK/ Normal CP only NACK

FIG. 13 shows a PUCCH resource mapping structure for use in a ULphysical resource block (PRB). N_(RB) ^(UL) is the number of resourceblocks (RBs) for use in uplink (UL), and n_(PRB) is a physical resourceblock (PRB) number. PUCCH may be mapped to both edges of a UL frequencyblock. CQI resources may be mapped to a PRB located just after the edgeof a frequency band, and ACK/NACK may be mapped to this PRB.

PUCCH format 1 may be a control channel used for SR transmission. SR(Scheduling Request) may be transmitted in such a manner that SR isrequested or not requested.

PUCCH format 1a/1b is a control channel used for ACK/NACK transmission.In the PUCCH format 1a/1b, a symbol modulated using the BPSK or QPSKmodulation scheme is multiplied by a CAZAC sequence of length 12. Uponcompletion of the CAZAC sequence multiplication, the resultant symbol isblockwise-spread as an orthogonal sequence. A Hadamard sequence oflength 4 is applied to general ACK/NACK information, and a DFT (DiscreteFourier Transform) sequence of length 3 is applied to the shortenedACK/NACK information and a reference signal. A Hadamard sequence oflength 2 may be applied to the reference signal for the extended CP.

The UE may also transmit HARQ ACK/NACK and SR through the same subframe.For positive SR transmission, the UE may transmit HARQ ACK/NACKinformation through resources allocated for the SR. For negative SRtransmission, the UE may transmit HARQ ACK/NACK information throughresources allocated for ACK/NACK information.

PUCCH format 2/2a/2b will hereinafter be described in detail. PUCCHformat 2/2a/2b is a control channel for transmitting channel measurementfeedback (CQI, PMI, RI).

The PUCCH format 2/2a/2b may support modulation based on a CAZACsequence, and a QPSK-modulated symbol may be multiplied by a CAZACsequence of length 12. Cyclic shift (CS) of the sequence may be changedbetween a symbol and a slot. For a reference signal (RS), orthogonalcovering may be used.

FIG. 14 shows a channel structure of a CQI information bit. The CQI bitmay include one or more fields. For example, the CQI bit may include aCQI field indicating a CQI index for MCS decision, a PMI fieldindicating an index of a precoding matrix of a codebook, and an RI fieldindicating rank.

Referring to FIG. 14( a), a reference signal (RS) may be loaded on twoSC-FDMA symbols spaced apart from each other by a predetermined distancecorresponding to 3 SC-FDMA symbol intervals from among 7 SC-FDMA symbolscontained in one slot, and CQI information may be loaded on theremaining 5 SC-FDMA symbols. The reason why two RSs may be used in oneslot is to support a high-speed UE. In addition, each UE may bediscriminated by a sequence. CQI symbols may be modulated in the entireSC-FDMA symbol, and the modulated CQI symbols may then be transmitted.The SC-FDMA symbol is composed of one sequence. That is, a UE performsCQI modulation using each sequence, and transmits the modulated result.

The number of symbols that can be transmitted to one TTI is set to 10,and CQI modulation is extended up to QPSK. If QPSK mapping is applied tothe SC-FDMA symbol, a CQI value of 2 bits may be loaded on the SC-FDMAsymbol, so that a CQI value of 10 bits may be assigned to one slot.Therefore, a maximum of 20-bit CQI value may be assigned to onesubframe. A frequency domain spreading code may be used to spread CQI ina frequency domain.

CAZAC sequence (for example, a ZC sequence) may be used as a frequencydomain spread code. In addition, another sequence having superiorcorrelation characteristics may be used as the frequency domain spreadcode. Specifically, CAZAC sequences having different cyclic shift (CS)values may be applied to respective control channels, such that theCAZAC sequences may be distinguished from one another. IFFT may beapplied to the frequency domain spread CQI.

FIG. 14( b) shows the example of PUCCH format 2/2a/2b transmission incase of the extended CP. One slot includes 6 SC-FDMA symbols. RS isassigned to one OFDM symbol from among 6 OFDM symbols of each slot, anda CQI bit may be assigned to the remaining 5 OFDM symbols. Except forthe six SC-FDMA symbols, the example of the normal CP of FIG. 14( a) maybe used without change.

Orthogonal covering applied to the RS of FIGS. 14( a) and 14(b) is shownin Table 2.

TABLE 2 Normal CP Extended CP [1 1] [1]

Simultaneous transmission of CQI and ACK/NACK information willhereinafter be described with reference to Table 15.

In case of the normal CP, CQI and ACK/NACK information can besimultaneously transmitted using PUCCH format 2a/2b. ACK/NACKinformation may be transmitted through a symbol where CQI RS istransmitted. That is, a second RS for use in the normal CP may bemodulated into an ACK/NACK symbol. In the case where the ACK/NACK symbolis modulated using the BPSK scheme as shown in the PUCCH format 1a, CQIRS may be modulated into the ACK/NACK symbol according to the BPSKscheme. In the case where the ACK/NACK symbol is modulated using theQPSK scheme as shown in the PUCCH format 1b, CQI RS may be modulatedinto the ACK/NACK symbol according to the QPSK scheme. On the otherhand, in case of the extended CP, CQI and ACK/NACK information aresimultaneously transmitted using the PUCCH format 2. For this purpose,CQI and ACK/NACK information may be joint-coded.

For details of PUCCH other than the above-mentioned description, the3GPP standard document (e.g., 3GPP TS36.211 5.4) may be referred to, anddetailed description thereof will herein be omitted for convenience ofdescription. However, it should be noted that PUCCH contents disclosedin the above-mentioned standard document can also be applied to a PUCCHused in various embodiments of the present invention without departingfrom the scope or spirit of the present invention.

Channel Status Information (CSI) Feedback

In order to correctly perform MIMO technology, the receiver may feedback a rank indicator (RI), a precoding matrix index (PMI) and a channelquality indicator (CQI) to the transmitter. RI, PMI and CQI may begenerically named Channel Status Information (CSI) as necessary.Alternatively, the term “CQI” may be used as the concept of channelinformation including RI, PMI and CQI.

FIG. 16 is a conceptual diagram illustrating a feedback of channelstatus information.

Referring to FIG. 16, MIMO transmission data from the transmitter may bereceived at a receiver over a channel (H). The receiver may select apreferred precoding matrix from a codebook on the basis of the receivedsignal, and may feed back the selected PMI to the transmitter. Inaddition, the receiver may measure a Signal-to-Interference plus NoiseRatio (SINR) of the reception (Rx) signal, calculate channel qualityinformation (CQI), and feed back the calculated CQI to the transmitter.In addition, the receiver may measure a Signal-to-Interference plusNoise Ratio (SINR) of the reception (Rx) signal, calculate a CQI, andfeed back the calculated SINR to the transmitter. In addition, thereceiver may feed back a rank indicator (RI) of the Rx signal to thetransmitter. The transmitter may determine the number of layers suitablefor data transmission to the receiver and time/frequency resources, MCS(Modulation and Coding Scheme), etc. using RI and CQI information fedback from the receiver. In addition, the receiver may transmit theprecoded Tx signal using the precoding matrix (W₁) indicated by a PMIfed back from the receiver over a plurality of antennas.

Channel status information will hereinafter be described in detail.

RI is information regarding a channel rank (i.e., the number of layersfor data transmission of a transmitter). RI may be determined by thenumber of allocated Tx layers, and may be acquired from associateddownlink control information (DCI).

PMI is information regarding a precoding matrix used for datatransmission of a transmitter. The precoding matrix fed back from thereceiver may be determined considering the number of layers indicated byRI. PMI may be fed back in case of closed-loop spatial multiplexing (SM)and large delay cyclic delay diversity (CDD). In the case of open-looptransmission, the transmitter may select a precoding matrix according topredetermined rules. A process for selecting a PMI for each rank (rank 1to 4) is as follows. The receiver may calculate a post processing SINRin each PMI, convert the calculated SINR into the sum capacity, andselect the best PMI on the basis of the sum capacity. That is, PMIcalculation of the receiver may be considered to be a process forsearching for an optimum PMI on the basis of the sum capacity. Thetransmitter that has received PMI feedback from the receiver may use aprecoding matrix recommended by the receiver. This fact may be containedas a 1-bit indicator in scheduling allocation information for datatransmission to the receiver. Alternatively, the transmitter may not usethe precoding matrix indicated by a PMI fed back from the transmitter.In this case, precoding matrix information used for data transmissionfrom the transmitter to the receiver may be explicitly contained in thescheduling allocation information. For details of PMI, the 3GPP standarddocument (e.g., 3GPP TS36.211) may be referred to.

CQI is information regarding channel quality. CQI may be represented bya predetermined MCS combination. CQI index may be given as shown in thefollowing table 3.

TABLE 3 CQI index modulation code rate × 1024 efficiency 0 out of range1 QPSK 78 0.1523 2 QPSK 120 0.2344 3 QPSK 193 0.3770 4 QPSK 308 0.6016 5QPSK 449 0.8770 6 QPSK 602 1.1758 7 16QAM 378 1.4766 8 16QAM 490 1.91419 16QAM 616 2.4063 10 64QAM 466 2.7305 11 64QAM 567 3.3223 12 64QAM 6663.9023 13 64QAM 772 4.5234 14 64QAM 873 5.1152 15 64QAM 948 5.5547

Referring to Table 3, CQI index may be represented by 4 bits (i.e., CQIindexes of 0˜15). Each CQI index may indicate a modulation scheme and acode rate.

A CQI calculation method will hereinafter be described. The followingassumptions (1) to (5) for allowing a UE to calculate a CQI index aredefined in the 3GPP standard document (e.g., 3GPP TS36.213).

(1) The first three OFDM symbols in one subframe are occupied by controlsignaling.

(2) Resource elements (REs) used by a primary synchronization signal, asecondary synchronization signal or a physical broadcast channel (PBCH)are not present.

(3) CP length of a non-MBSFN subframe is assumed.

(4) Redundancy version is set to zero (0).

(5) PDSCH transmission method may be dependent upon a currenttransmission mode (e.g., a default mode) configured in a UE.

(6) The ratio of PDSCH EPRE (Energy Per Resource Element) to acell-specific reference signal EPRE may be given with the exception ofρ_(A). (A detailed description of ρ_(A) may follow the followingassumption. Provided that a UE for an arbitrary modulation scheme may beset to a Transmission Mode 2 having four cell-specific antenna ports ormay be set to a Transmission Mode 3 having an RI of 1 and fourcell-specific antenna ports, ρ_(A) may be denoted byρ_(A)=P_(A)+Δ_(offset)+10 log₁₀(2)[dB]. In the remaining cases, inassociation with an arbitrary modulation method and the number ofarbitrary layers, PA may be denoted by ρ_(A)=P_(A)+Δ_(offset)[dB].Δ_(offset) is given by a nomPDSCH-RS-EPRE-Offset parameter configured byhigher layer signaling.)

Definition of the above-mentioned assumptions (1) to (5) may indicatethat a CQI includes not only a CQI but also various information of acorresponding UE. That is, different CQI indexes may be fed backaccording to a throughput or performance of the corresponding UE at thesame channel quality, so that it is necessary to define a predeterminedreference for the above-mentioned assumption.

The UE may receive a downlink reference signal (DL RS) from an eNB, andrecognize a channel status on the basis of the received DL RS. In thiscase, the RS may be a common reference signal (CRS) defined in thelegacy 3GPP LTE system, and may be a Channel Status InformationReference Signal (CSI-RS) defined in a system (e.g., 3GPP LTE-A system)having an extended antenna structure. The UE may satisfy the assumptiongiven for CQI calculation at a channel recognized through a referencesignal (RS), and at the same time calculate a CQI index in which a BlockError Rate (BLER) is not higher than 10%. The UE may transmit thecalculated CQI index to the eNB. The UE may not apply a method forimproving interference estimation to a CQI index calculation process.

The process for allowing the UE to recognize a channel status andcalculate an appropriate MCS may be defined in various ways in terms ofUE implementation. For example, the UE may calculate a channel status oran effective SINR using a reference signal (RS). In addition, thechannel status or the effective SINR may be measured on the entiresystem bandwidth (also called ‘Set S’) or may also be measured on somebandwidths (specific subband or specific RB). The CQI for the set S maybe referred to as a Wideband WB CQI, and the CQI for some bandwidths maybe referred to as a subband (SB) CQI. The UE may calculate the highestMCS on the basis of the calculated channel status or effective SINR. Thehighest MCS may indicate an MCS that satisfies the CQI calculationassumption without exceeding a transport block error rate of 10% duringthe decoding. The UE may determine a CQI index related to the calculatedMCS, and may report the determined CQI index to the eNB.

Further, CQI-only transmission may be considered in which a UE transmitsonly a CQI. Aperiodic CQI transmission may be event-triggered uponreceiving a request from the eNB. Such request from the eNB may be a CQIrequest defined by one bit of DCI format 0. In addition, for CQI-onlytransmission, MCS index (I_(MCS)) of 29 may be signaled as shown in thefollowing table 4. In this case, the CQI request bit of the DCI format 0is set to 1, transmission of 4 RBs or less may be configured, RedundancyVersion 1 (RV1) is indicated in PUSCH data retransmission, and amodulation order (Q_(m)) may be set to 2. In other words, in the case ofCQI-only transmission, only a QPSK (Quadrature Phase Shift Keying)scheme may be used as a modulation scheme.

TABLE 4 Modulation TBS Redundancy MCS Index Order Index Version I_(MCS)Q_(m)′ I_(TBS) rv_(idx) 0 2 0 0 1 2 1 0 2 2 2 0 3 2 3 0 4 2 4 0 5 2 5 06 2 6 0 7 2 7 0 8 2 8 0 9 2 9 0 10 2 10 0 11 4 10 0 12 4 11 0 13 4 12 014 4 13 0 15 4 14 0 16 4 15 0 17 4 16 0 18 4 17 0 19 4 18 0 20 4 19 0 216 19 0 22 6 20 0 23 6 21 0 24 6 22 0 25 6 23 0 26 6 24 0 27 6 25 0 28 626 0 29 reserved 1 30 2 31 3

The CQI reporting operation will hereinafter be described in detail.

In the 3GPP LTE system, when a DL reception entity (e.g., UE) is coupledto a DL transmission entity (e.g., eNB), a Reference Signal ReceivedPower (RSRP) and a Reference Signal Received Quality (RSRQ) that aretransmitted via downlink are measured at an arbitrary time, and themeasured result may be periodically or event-triggeredly reported to theeNB.

In a cellular OFDM wireless packet communication system, each UE mayreport DL channel information based on a DL channel condition viauplink, and the eNB may determine time/frequency resources and MCS(Modulation and Coding Scheme) so as to transmit data to each UE usingDL channel information received from each UE.

In case of the legacy 3GPP LTE system (e.g., 3GPP LTE Release-8 system),such channel information may be composed of Channel Quality Indication(CQI), Precoding Matrix Indicator (PMI), and Rank Indication (RI). Allor some of CQI, PMI and RI may be transmitted according to atransmission mode of each UE. CQI may be determined by the receivedsignal quality of the UE. Generally, CQI may be determined on the basisof DL RS measurement. In this case, a CQI value actually applied to theeNB may correspond to an MCS in which the UE maintains a Block ErrorRate (BLER) of 10% or less at the measured Rx signal quality and at thesame time has a maximum throughput or performance. In addition, suchchannel information reporting scheme may be divided into periodicreporting and aperiodic reporting upon receiving a request from the eNB.

Information regarding the aperiodic reporting may be assigned to each UEby a CQI request field of 1 bit contained in uplink schedulinginformation sent from the eNB to the UE. Upon receiving the aperiodicreporting information, each UE may transmit channel informationconsidering the UE's transmission mode to the eNB over a physical uplinkshared channel (PUSCH). If necessary, RI and CQI/PMI need not betransmitted over the same PUSCH.

In case of the aperiodic reporting, a cycle in which channel informationis transmitted via an upper layer signal, an offset of the correspondingperiod, etc. may be signaled to each UE in units of a subframe, andchannel information considering a transmission (Tx) mode of each UE maybe transmitted to the eNB over a physical uplink control channel (PUCCH)at intervals of a predetermined time. In the case where UL transmissiondata is present in a subframe to which channel information istransmitted at intervals of a predetermined time, the correspondingchannel information may be transmitted together with data over not aPUCCH but a PUSCH together. In case of the periodic reporting over aPUCCH, a limited number of bits may be used as compared to PUSCH. RI andCQI/PMI may be transmitted over the same PUSCH. If the periodicreporting collides with the aperiodic reporting, only the aperiodicreporting may be performed within the same subframe.

In order to calculate a WB CQI/PMI, the latest transmission RI may beused. In a PUCCH reporting mode, RI may be independent of another RI foruse in a PUSCH reporting mode. RI may be effective only at CQI/PMI foruse in the corresponding PUSCH reporting mode.

The CQI/PMI/RI feedback type for the PUCCH reporting mode may beclassified into four feedback types (Type 1 to Type 4). Type 1 is CQIfeedback for a user-selected subband. Type 2 is WB CQI feedback and WBPMI feedback. Type 3 is RI feedback. Type 4 is WB CQI feedback.

Referring to Table 5, in the case of periodic reporting of channelinformation, a reporting mode is classified into four reporting modes(Modes 1-0, 1-1, 2-0 and 2-1) according to CQI and PMI feedback types.

TABLE 5 PMI Feedback Type No PMI (OL, TD, single-antenna) Single PMI(CL) CQI Wideband Mode 1-0 Mode 1-1 Feedback RI (only for Open-Loop SM)RI Type One Wideband CQI (4 bit) Wideband CQI (4 bit) when RI > 1, CQIof first codeword Wideband spatial CQI (3 bit) for RI > 1 Wideband PMI(4 bit) UE Mode 2-0 Mode 2-1 Selected RI (only for Open-Loop SM) RIWideband CQI (4 bit) Wideband CQI (4 bit) Best-1 CQI (4 bit) in each BPWideband spatial CQI (3 bit) for RI > 1 Best-1 indicator(L-bit label)Wideband PMI (4 bit) when RI > 1, CQI of first codeword Best-1 CQI (4bit) 1 in each BP Best-1 spatial CQI (3 bit) for RI > 1 Best-1 indicator(L-bit label)

The reporting mode is classified into a wideband (WB) CQI and a subband(SB) CQI according to a CQI feedback type. The reporting mode isclassified into a No-PMI and a Single PMI according to transmission ornon-transmission of PMI. As can be seen from Table 5, ‘NO PMI’ maycorrespond to an exemplary case in which an Open Loop (OL), a TransmitDiversity (TD), and a single antenna are used, and ‘Single PMI’ maycorrespond to an exemplary case in which a closed loop (CL) is used.

Mode 1-0 may indicate an exemplary case in which PMI is not transmittedbut only WB CQI is transmitted. In case of Mode 1-0, RI may betransmitted only in the case of Spatial Multiplexing (SM), and one WBCQI denoted by 4 bits may be transmitted. If RI is higher than ‘1’, aCQI for a first codeword may be transmitted. In case of Mode 1-0,Feedback Type 3 and Feedback Type 4 may be multiplexed at different timepoints within the predetermined reporting period, and then transmitted.The above-mentioned Mode 1-0 transmission scheme may be referred to asTime Division Multiplexing (TDM)-based channel information transmission.

Mode 1-1 may indicate an exemplary case in which a single PMI and a WBCQI are transmitted. In this case, 4-bit WB CQI and 4-bit WB PMI may betransmitted simultaneously with RI transmission. In addition, if RI ishigher than ‘1’, 3-bit WB Spatial Differential CQI may be transmitted.In case of transmission of two codewords, the WB spatial differentialCQI may indicate a differential value between a WB CQI index forCodeword 1 and a WB CQI index for Codeword 2. These differential valuesmay be assigned to the set {−4, −3, −2, −1, 0, 1, 2, 3}, and eachdifferential value may be assigned to any one of values contained in theset and be represented by 3 bits. In case of Mode 1-1, Feedback Type 2and Feedback Type 3 may be multiplexed at different time points withinthe predetermined reporting period, and then transmitted.

Mode 2-0 may indicate that no PMI is transmitted and a CQI of aUE-selected band is transmitted. In this case, RI may be transmittedonly in case of open loop spatial multiplexing (OL SM), a WB CQI denotedby 4 bits may be transmitted. In each Bandwidth Part (BP), Best-1 CQImay be transmitted, and Best-1 CQI may be denoted by 4 bits. Inaddition, an indicator of L bits indicating Best-1 may be furthertransmitted. If RI is higher than ‘1’, CQI for a first codeword may betransmitted. In case of Mode 2-0, the above-mentioned feedback type 1,feedback type 3, and feedback type 4 may be multiplexed at differenttime points within a predetermined reporting period, and thentransmitted.

Mode 2-1 may indicate an exemplary case in which a single PMI and a CQIof a UE-selected band are transmitted. In this case, WB CQI of 4 bits,WB spatial differential CQI of 3 bits, and WB PMI of 4 bits aretransmitted simultaneously with RI transmission. In addition, a Best-1CQI of 4 bits and a Best-1 indicator of L bits may be simultaneouslytransmitted at each bandwidth part (BP). If RI is higher than ‘1’, aBest-1 spatial differential CQI of 3 bits may be transmitted. Duringtransmission of two codewords, a differential value between a Best-1 CQIindex of Codeword 1 and a Best-1 CQI index of Codeword 2 may beindicated. In Mode 2-1, the above-mentioned feedback type 1, feedback 2,and feedback type 3 may be multiplexed at different time points within apredetermined reporting period, and then transmitted.

In the UE selected SB CQI reporting mode, the size of BP (BandwidthPart) subband may be defined by the following table 6.

TABLE 6 System Bandwidth Subband Size k Bandwidth Parts N_(RB) ^(DL)(RBs) (J) 6-7 NA NA  8-10 4 1 11-26 4 2 27-63 6 3  64-110 8 4

Table 6 shows a bandwidth part (BP) configuration and the subband sizeof each BP according to the size of a system bandwidth. A UE may selecta preferred subband within each BP, and calculate a CQI for thecorresponding subband. In Table 6, if the system bandwidth is set to 6or 7, this means no application of both the subband size and the numberof bandwidth parts (BPs). That is, the system bandwidth of 6 or 7 meansapplication of only WB CQI, no subband state, and a BP of 1.

FIG. 17 shows an example of a UE selected CQI reporting mode.

N_(RB) ^(DL) the number of RBs of the entire bandwidth. The entirebandwidth may be divided into N CQI subbands (1, 2, 3, . . . , N). OneCQI subband may include k RBs defined in Table 6. If the number of RBsof the entire bandwidth is not denoted by an integer multiple of k, thenumber of RBs contained in the last CQI subband (i.e., the N-th CQIsubband) may be determined by the following equation 14.N _(RB) ^(DL) =k·└N _(RB) ^(DL) /k┘  [Equation 14]

In Equation 14, └ ┘ represents a floor operation, and └x┘ or floor(x)represents a maximum integer not higher than ‘x’.

In addition, N_(J) CQI subbands construct one BP, and the entirebandwidth may be divided into J BPs. UE may calculate a CQI index forone preferred Best-1 CQI subband in contained in one BP, and transmitthe calculated CQI index over a PUCCH. In this case, a Best-1 indicatorindicating which a Best-1 CQI subband is selected in one BP may also betransmitted. The Best-1 indicator may be composed of L bits, and L maybe represented by the following equation 15.L=┌log₂ N _(J)┐  [Equation 15]

In Equation 15, ┌ ┐ may represent a ceiling operation, and ┌x┐ orceiling(x) may represent a minimum integer not higher than ‘x’.

In the above-mentioned UE selected CQI reporting mode, a frequency bandfor CQI index calculation may be determined. Hereinafter, a CQItransmission cycle will hereinafter be described in detail.

Each UE may receive information composed of a combination of atransmission cycle of channel information and an offset from an upperlayer through RRC signaling. The UE may transmit channel information toan eNB on the basis of the received channel information transmissioncycle information.

FIG. 18 is a conceptual diagram illustrating a method for enabling a UEto periodically transmit channel information. For example, if a UEreceives combination information in which a channel informationtransmission cycle is set to 5 and an offset is set to 1, the UEtransmits channel information in units of 5 subframes, one subframeoffset is assigned in the increasing direction of a subframe index onthe basis of the 0^(th) subframe, and channel information may beassigned over a PUCCH. In this case, the subframe index may be comprisedof a combination of a system frame number (n_(f)) and 20 slot indexes(n_(s), 0˜19) present in the system frame. One subframe may be comprisedof 2 slots, such that the subframe index may be represented by10×n_(f)+floor(n_(s)/2).

One type for transmitting only WB CQI and the other type fortransmitting both WB CQI and SB CQI may be classified according to CQIfeedback types. In case of the first type for transmitting only the WBCQI, WB CQI information for the entire band is transmitted at a subframecorresponding to each CQI transmission cycle. The WB periodic CQIfeedback transmission cycle may be set to any of 2, 5, 10, 16, 20, 32,40, 64, 80, or 160 ms or no transmission of the WB periodic CQI feedbacktransmission cycle may be established. In this case, if it is necessaryto transmit PMI according to the PMI feedback type of Table 5, PMIinformation is transmitted together with CQI. In case of the second typefor transmitting both WB CQI and SB CQI, WB CQI and SB CQI may bealternately transmitted.

FIG. 19 is a conceptual diagram illustrating a method for transmittingboth WB CQI and SB CQI according to an embodiment of the presentinvention. FIG. 19 shows an exemplary system comprised of 16 RBs. If asystem frequency band is comprised of 16 RBs, for example, it is assumedthat two bandwidth parts (BPs) (BP0 and BP1) may be configured, each BPmay be composed of 2 subbands (SBs) (SB0 and SB1), and each SB may becomposed of 4 RBs. In this case, as previously stated in Table 6, thenumber of BPs and the size of each SB are determined according to thenumber of RBs contained in the entire system band, and the number of SBscontained in each BP may be determined according to the number of RBs,the number of BPs and the size of SB.

In case of the type for transmitting both WB CQI and SB CQI, the WB CQIis transmitted to the CQI transmission subframe. In the nexttransmission subframe, a CQI of one SB (i.e., Best-1) having a goodchannel state from among SB0 and SB1 at BP0 and an index (i.e., Best-1indicator) of the corresponding SB are transmitted. In the further nexttransmission subframe, a CQI of one SB (i.e., Best-1) having a goodchannel state from among SB0 and SB1 at BP1 and an index (i.e., Best-1indicator) of the corresponding SB are transmitted. After transmittingthe WB CQI, CQIs of individual BPs are sequentially transmitted. In thiscase, CQI of a BP located between a first WB CQI transmitted once and asecond WB CQI to be transmitted after the first WB CQI may besequentially transmitted one to four times. For example, if the CQI ofeach BP is transmitted once during a time interval between two WB CQIs,CQIs may be transmitted in the order of WB CQI→BP0 CQI→BP1 CQI→WB CQI.In another example, if the CQI of each BP is transmitted four timesduring a time interval between two WB CQIs, CQIs may be transmitted inthe order of WB CQI→BP0 CQI→BP1 CQI→BP0 CQI→BP1 CQI→BP0 CQI→BP1 CQI→BP0CQI→BP1 CQI→WB CQI. Information about the number of sequentialtransmission times of BP CQI during a time interval between two WB CQIsis signaled through a higher layer. Irrespective of WB CQI or SB CQI,the above-mentioned information about the number of sequentialtransmission times of BP CQI may be transmitted through a PUCCH in asubframe corresponding to information of a combination of channelinformation transmission cycle signaled from the higher layer of FIG. 18and an offset.

In this case, if PMI also needs to be transmitted according to the PMIfeedback type, PMI information and CQI must be simultaneouslytransmitted. If PUSCH for UL data transmission is present in thecorresponding subframe, CQI and PMI can be transmitted along with datathrough PUSCH instead of PUCCH.

FIG. 20 is a conceptual diagram illustrating an exemplary CQItransmission scheme when both WB CQI and SB CQI are transmitted. In moredetail, provided that combination information in which a channelinformation transmission cycle is set to 5 and an offset is set to 1 issignaled as shown in FIG. 18, and BP information between two WB CQI/PMIparts is sequentially transmitted once, FIG. 20 shows the example ofchannel information transmission operation of a UE.

On the other hand, in case of RI transmission, RI may be signaled byinformation of a combination of one signal indicating how many WBCQI/PMI transmission cycles are used for RI transmission and an offsetof the corresponding transmission cycle. In this case, the offset may bedefined as a relative offset for a CQI/PMI transmission offset. Forexample, provided that an offset of the CQI/PMI transmission cycle isset to 1 and an offset of the RI transmission cycle is set to zero, theoffset of the RI transmission cycle may be identical to that of theCQI/PMI transmission cycle. The offset of the RI transmission cycle maybe defined as a negative value or zero.

FIG. 21 is a conceptual diagram illustrating transmission of WB CQI, SBCQI and RI. In more detail, FIG. 21 shows that, under CQI/PMItransmission of FIG. 20, an RI transmission cycle is one time the WBCQI/PMI transmission cycle and the offset of RI transmission cycle isset to ‘−1’. Since the RI transmission cycle is one time the WB CQI/PMItransmission cycle, the RI transmission cycle has the same time cycle. Arelative difference between the RI offset value ‘−1’ and the CQI offset‘1’ of FIG. 20 is set to ‘−1’, such that RI can be transmitted on thebasis of the subframe index ‘0’.

In addition, provided that RI transmission overlaps with WB CQI/PMItransmission or SB CQI/PMI transmission, WB CQI/PMI or SB CQI/PMI maydrop. For example, provided that the RI offset is set to ‘0’ instead of‘−1’, the WB CQI/PMI transmission subframe overlaps with the RItransmission subframe. In this case, WB CQI/PMI may drop and RI may betransmitted.

By the above-mentioned combination, CQI, PMI, and RI may be transmitted,and such information may be transmitted from each UE by RRC signaling ofa higher layer. The BS (or eNB) may transmit appropriate information toeach UE in consideration of a channel situation of each UE and adistribution situation of UEs contained in the BS (or eNB).

Meanwhile, payload sizes of SB CQI, WB CQI/PMI, RI and WB CQI inassociation with the PUCCH report type may be represented by thefollowing table 7.

TABLE 7 PUCCH Reporting Modes Mode Mode Mode Mode PUCCH 1-1 2-1 1-0 2-0Report (bits/ (bits/ (bits/ (bits/ Type Reported Mode State BP) BP) BP)BP) 1 Sub-band RI = 1 NA 4 + L NA 4 + L CQI RI > 1 NA 7 + L NA 4 + L 2Wideband 2 TX Antennas RI = 1 6 6 NA NA CQI/PMI 4 TX Antennas RI = 1 8 8NA NA 2 TX Antennas RI > 1 8 8 NA NA 4 TX Antennas RI > 1 11  11  NA NA3 RI 2-layer spatial 1 1 1 1 multiplexing 4-layer spatial 2 2 2 2multiplexing 4 Wideband RI = 1 or RI > 1 NA NA 4 4 CQI

Aperiodic transmission of CQI, PMI and RI over a PUSCH will hereinafterbe described.

In case of the aperiodic reporting, RI and CQI/PMI may be transmittedover the same PUSCH. In case of the aperiodic reporting mode, RIreporting may be effective only for CQI/PMI reporting in thecorresponding aperiodic reporting mode. CQI-PMI combinations capable ofbeing supported to all the rank values are shown in the following table8.

TABLE 8 PMI Feedback Type No PMI (OL, TD, single-antenna) with PMI (CL)PUSCH CQI Wideband Mode 1-2: Multiple PMI Feedback Type (Wideband CQI)RI 1^(st) Wideband CQI (4 bit) 2^(nd) Wideband CQI (4 bit) if RI > 1subband PMIs on each subband UE Selected Mode 2-0 Mode 2-2: Multiple PMI(Subband CQI) RI (only for Open-Loop SM) RI Wideband CQI (4 bit) +Best-M CQI (2 bit) 1^(st) Wideband CQI (4 bit) + Best-M CQI(2 bit)Best-M index 2^(nd) Wideband CQI (4 bit) + Best-M CQI(2 bit) when RI >1, CQI of first codeword if RI > 1 Wideband PMI + Best-M PMI Best-Mindex Higher layer-configured Mode 3-0 Mode 3-1: Single PMI (subbandCQI) RI (only for Open-Loop SM) RI Wideband CQI (4 bit) + subband CQI (2bit) 1^(st) Wideband CQI (4 bit) + subband CQI when RI > 1, CQI of firstcodeword (2 bit) 2^(nd) Wideband CQI (4 bit) + subband CQI (2 bit) ifRI > 1 Wideband PMI

Mode 1-2 of Table 8 may indicate a WB feedback. In Mode 1-2, a preferredprecoding matrix for each subband may be selected from a codebook subseton the assumption of transmission only in the corresponding subband. TheUE may report one WB CQI at every codeword, and WB CQI may be calculatedon the assumption that data is transmitted on subbands of the entiresystem bandwidth (Set S) and the corresponding selected precoding matrixis used on each subband. The UE may report the selected PMI for eachsubband. In this case, the subband size may be given as shown in thefollowing table 9. In Table 9, if the system bandwidth is set to 6 or 7,this means no application of the subband size. That is, the systembandwidth of 6 or 7 means application of only WB CQI and no subbandstate.

TABLE 9 System Bandwidth Subband Size N_(RB) ^(DL) (k) 6-7 NA  8-10 411-26 4 27-63 6  64-110 8

In Table 8, Mode 3-0 and Mode 3-1 show a subband feedback configured bya higher layer (also called an upper layer).

In Mode 3-0, the UE may report a WB CQI value calculated on theassumption of data transmission on the set-S (total system bandwidth)subbands. The UE may also report one subband CQI value for each subband.The subband CQI value may be calculated on the assumption of datatransmission only at the corresponding subband. Even in the case ofRI>1, WB CQI and SB CQI may indicate a channel quality for Codeword 1.

In Mode 3-1, a single precoding matrix may be selected from a codebooksubset on the assumption of data transmission on the set-S subbands. TheUE may report one SB CQI value for each codeword on each subband. The SBCQI value may be calculated on the assumption of a single precodingmatrix used in all subbands and data transmission on the correspondingsubband. The UE may report a WB CQI value for each codeword. The WB CQIvalue may be calculated on the assumption of a single precoding matrixused in all the subbands and data transmission on the set-S subbands.The UE may report one selected precoding matrix indicator. The SB CQIvalue for each codeword may be represented by a differential WB CQIvalue using a 2-bit subband differential CQI offset. That is, thesubbband differential CQI offset may be defined as a differential valuebetween a SB CQI index and a WB CQI index. The subband differential CQIoffset value may be assigned to any one of four values {−2, 0, +1, +2}.In addition, the subband size may be given as shown in the followingtable 7.

In Table 8, Mode 2-0 and Mode 2-2 illustrate a UE selected subbandfeedback. Mode 2-0 and Mode 2-2 illustrate reporting of best-M averages.

In Mode 2-0, the UE may select the set of M preferred subbands (i.e.,best-M) from among the entire system bandwidth (set S). The size of onesubband may be given as k, and k and M values for each set-S range maybe given as shown in the following table 10. In Table 10, if the systembandwidth is set to 6 or 7, this means no application of both thesubband size and the M value. That is, the system bandwidth of 6 or 7means application of only WB CQI and no subband state.

The UE may report one CQI value reflecting data transmission only at thebest-M subbands (i.e., M selected subbands). This CQI value may indicatea CQI for Codeword 1 even in the case of RI>1. In addition, the UE mayreport a WB CQI value calculated on the assumption of data transmissionon the set-S subbands. The WB CQI value may indicate a CQI for Codeword1 even in the case of RI>1.

TABLE 10 System Bandwidth N_(RB) ^(DL) Subband Size k (RBs) M 6-7 NA NA 8-10 2 1 11-26 2 3 27-63 3 5  64-110 4 6

In Mode 2-2, the UE may select the set of M preferred subbands (i.e.,best-M) from among the set-S subbands (where the size of one subband isset to k). Simultaneously, one preferred precoding matrix may beselected from among a codebook subset to be used for data transmissionon the M selected subbands. The UE may report one CQI value for eachcodeword on the assumption that data transmission is achieved on Mselected subbands and selection precoding matrices are used in each ofthe M subbands. The UE may report an indicator of one precoding matrixselected for the M subbands. In addition, one precoding matrix (i.e., aprecoding matrix different from the precoding matrix for theabove-mentioned M selected subbands) may be selected from among thecodebook subset on the assumption that data transmission is achieved onthe set-S subbands. The UE may report a WB CQI, that is calculated onthe assumption that data transmission is achieved on the set-S subbandsand one precoding matrix is used in all the subbands, at every codeword.The UE may report an indicator of the selected one precoding matrix inassociation with all subbands.

In association with entirety of UE-selected subband feedback modes (Mode2-0 and Mode 2-2), the UE may report the positions of M selectedsubbands using a combination index (r), where r may be represented bythe following equation 16.

$\begin{matrix}{r = {\sum\limits_{i = 0}^{M - 1}\;\left\langle \begin{matrix}{N - S_{i}} \\{M - i}\end{matrix} \right\rangle}} & \left\lbrack {{Equation}\mspace{14mu} 16} \right\rbrack\end{matrix}$

In Equation 16, the set {s_(i)}_(i=0) ^(M−1), (1≦s_(i)≦N, s_(i)<s_(i+1))may include M sorted subband indexes. In Equation 14,

$\quad\left\langle \begin{matrix}x \\y\end{matrix} \right\rangle$may indicate an extended binomial coefficient, which is set to

$\quad\begin{pmatrix}x \\y\end{pmatrix}$in case of x≧y and is set to zero (0) in case of x<y. Therefore, r mayhave a unique label and may be denoted by

$r \in {\left\{ {0,\ldots\mspace{14mu},{\begin{pmatrix}N \\M\end{pmatrix} - 1}} \right\}.}$

In addition, a CQI value for M selected subbands for each codeword maybe denoted by a relative differential value in association with a WBCQI. The relative differential value may be denoted by a differentialCQI offset level of 2 bits, and may have a value of ‘CQI index—WB CQIindex’ of M selected subbands. An available differential CQI value maybe assigned to any one of four values {+1, +2, +3, +4}.

In addition, the size(k) of supported subbands and the M value may begiven as shown in Table 10. As shown in Table 10, k or M may be given asa function of a system bandwidth.

A label indicating the position of each of M selected subbands (i.e.,best-M subbands) may be denoted by L bits, where L is denoted by

$L = {\left\lceil {\log_{2}\begin{pmatrix}N \\M\end{pmatrix}} \right\rceil.}$

Feedback Information for Multiple MIMO Transmission Modes

As described above, Channel Status Information (CSI) is required forMIMO transmission. The CSI may be fed back from the receiver to thetransmitter. The transmitter may acquire a precoding weight, that iscapable of being adaptively used in response to a channel state, fromthe CSI. In addition, the transmitter may acquire signal transmissioninformation from the CSI modified by the precoding weight to be used forMIMO transmission. For example, the signal transmission information mayinclude a modulation order, a coding rate, a transport block size, ascheduling band, etc.

The receiver may obtain channel status information (CSI) between thetransmitter and the receiver using a reference signal (RS) received fromthe transmitter, and may feed back (or report) the obtained CSI to thetransmitter. In this case, a variety of methods may be used to reducethe amount of feedback CSI. For example, a channel qualityinformation/index (CQI), a precoding matrix index (PMI), a rankindicator (RI), etc. can be represented by quantized bits, such that theamount of feedback information is reduced, resulting in theimplementation of efficient transmission.

Specifically, information regarding a rank suitable for MIMOtransmission is changed according to long term fading, such that theabove-mentioned rank information is not changed for a relatively longerterm as compared to other CSI. On the other hand, PMI or CQI reflects achannel state abruptly changed by short-term fading, such that it ischanged for a relatively short time. Accordingly, RI may be reported fora relatively longer term as compared to PMI/CQI, and the PMI and CQI maybe reported for a relatively short term as compared to the RI. Inaddition, PMI and CQI are determined according to a rank used fortransmission, such that the PMI and CQI are calculated on the basis ofthe determined RI until reaching the next RI report period.

As described above, there is a need for a rank value to be firstdetermined when calculating channel status information (CSI). The rankvalue may be determined considering a MIMO transmission scheme. The MIMOtransmission method may be classified into a Multi-User MIMO (MU-MIMO)and a Single-User MIMO (SU-MIMO). If a spatial channel capable of beingcreated through multiple antennas is assigned to multiple users, thismeans the MU-MIMO. In contrast, if all spatial channels are assigned toa single user, this means SU-MIMO.

The MU-MIMO transmission scheme can be classified into a method forusing a non-unitary matrix such as Dirty Paper Coding (DPC), ZeroForcing, etc. and a method for using a unitary precoding weight such asa Per-User Unitary Rate Control (PU2RC). The two methods arecharacterized in that the precoding weight calculated on the basis ofthe limited transmission rank is reported to the transmitter from theviewpoint of a single user. For example, a multi-antenna transmitterincluding M transmission (Tx) antennas can generate a maximum of 8spatial channels and can transmit signals. The number of spatialchannels capable of being assigned to the receiver participating inMU-MIMO transmission may be set to M or less. In this case, a maximumnumber of spatial channels assigned to each user is limited to N (whereN<M), such that spatial channels of N or less may be received. Assumingthat a maximum of N transport spatial channels can be assigned to theUE, the UE selects a rank that is most appropriate for transmission.That is, the UE may select the most appropriate rank from among the N orless ranks (i.e., 1 to N ranks). The precoding weight and the channelquality information (CQI) can be calculated according to the selectedrank.

For example, if the number of spatial channels assigned to one receiveris limited to 2, the receiver can measure channel state information(CSI) on the assumption that one or two spatial channels can be assignedto the receiver. In this case, the amount of channel status informationthat must be measured and reported by the receiver can be greatlyreduced. That is, rank information is limited to N or 2, such that thenumber of required bits is reduced from log 2(N) to log 2(2).

PMI amount is determined according to the defined codebook set. Assumingthat L codebook sets from Rank 1 to Rank N are defined and K (where K<L)codebook sets from Rank 1 to Rank 2 are defined, the amount of feedbackinformation requisite for PMI reporting in case of a maximum ranklimited to N˜2 is reduced.

CQI must be calculated according to each codeword (CW). Provided that asystem having multiple codewords (MCW) includes a maximum of 2 CWs onRank-2 transmission, 2 CQIs should be reported for transmission ofRank-2 or higher. Provided that a maximum of 2 spatial channels areassigned, the same amount of CQI (i.e., 2 CQIs) may be reported.

The transmitter can calculate CQI in consideration of the number oftransmission layers. Provided that Rank-2 is used in MCW transmission,the second layer calculates SINR in consideration of interference whencalculating a CQI of a CW transmitted through a first layer. Similarly,the number of spatial channels simultaneously created by the transmitteris recognized by the receiver, the receiver measures channels statusinformation (CSI) appropriate for the maximum number of spatial channelscreated by the transmitter. In this case, the accuracy of CQI may beincreased. For example, provided that a maximum of 2 spatial channelsare formed by the transmitter and each spatial channel is assigned totwo users, the receiver may calculate the CQI on the assumption thatthere is an interference layer in CQI calculation.

On the other hand, SU-MIMO transmission is characterized in that oneuser uses all spatial channels created by the transmitter. The receivermay report rank information appropriate for transmission to a basestation (BS), and the receiver may report PMI and CQI calculated on thebasis of the rank information. For example, provided that a maximumnumber of spatial channels created by the transmitter is set to N, thereceiver selects a transmission rank capable of obtaining the highesttransmission efficiency from among 1 to N ranks, and reports theselected rank to an eNode B.

The transmitter can simultaneously support SU-MIMO transmission andMU-MIMO transmission. Specialized control signals may be requested forindividual SU-MIMO and MU-MIMO transmission. For example, a maximum of Nranks may be received in SU-MIMO transmission, and the transmitter forMU-MIMO transmission may generate a maximum of N spatial channels. Ifthe receiver considers a maximum of N spatial channels as the effectivespatial channels corresponding to individual users, a control signaloptimized for each transmission mode may be transmitted. In this case,the transmitter transmits indication information regarding thetransmission mode to the receiver, such that the receiver maypre-recognize which transmission mode is to be used for signaltransmission of the transmitter. Thereafter, a control signal suitablefor the pre-recognized information is transmitted, such that SU-MIMOtransmission and MU-MIMO transmission can be simultaneously supported.

On the other hand, the transmitter does not provide indication messagesof the SU-MIMO transmission mode and the MU-MIMO transmission mode tothe receiver, such that the transmitter may allow the receiver torecognize any one of the two transmission modes and decode correspondingdata. In this case, the transmitter may inform the receiver of thenumber of layers that must be received by a current UE. In this case, itis impossible for the UE to identify the SU-MIMO mode and the MU-MIMOmode. Therefore, it is possible to support MIMO transmission using thesame control signal. However, there is a need for the receiver to reportdifferent feedback information to the transmitter so as to supportSU-MIMO and MU-MIMO. For example, in order to support SU-MIMOtransmission, a transmission rank most appropriate for transmission maybe reported in consideration of a maximum number of spatial channelscapable of being generated in the transmitter. To support MU-MIMOtransmission, a rank most appropriate for transmission may be selectedand reported from among the restricted ranks in consideration ofreception of a limited number of layers from the viewpoint of thereceiver.

Multi-Rank PMI Feedback

In a feedback method for allowing a system supporting the extendedantenna configuration to smoothly support multiple MIMO modes,multi-rank PMI feedback may be used.

For example, PMI may be determined on the assumption that a receiver isscheduled to receive r layers from an eNode B during SU-MIMO rank-rtransmission and performs rank-r SU-MIMO transmission. On the otherhand, although one receiver can receive one layer during MU-MIMOtransmission, the transmitter may actually transmit multiple layers.

The multi-rank PMI feedback may indicate that a PMI of Rank-r is usedfor SU-MIMO mode transmission and the restricted rank (for example,Rank-1 or Rank-2) is used for MU-MIMO mode transmission. For example, itshould be noted that a Rank-r PMI based on SU-MIMO can be fed backduring Rank-r SU-MIMO transmission. Otherwise, PMI/CQI having therestricted rank (for example, Rank-1 or Rank-2) based on the SU-MIMOassumption may be fed back to MU-MIMO pairing. A method of using a PMIhaving the restricted rank (or low rank) will hereinafter be describedin detail.

A restricted PMI of a low rank value (Rank-1 or Rank-2) is appended tothe regular rank-r PMI so as to facilitate dynamic switching between theSU-MIMO mode and the MU-MIMO mode. In order to support dynamicSU-MIMO/MU-MIMO switching in all ranks from Rank-1 to Rank-8, a singletransmission mode for Ranks 1 to 8 has to support dynamic SU-MIMO andMU-MIMO switching on a per subframe basis. In other words, the same UEfeedback (up to a Rank-8 PMI/CQI) shall be used in both SU-MIMOscheduling and MU-MIMO scheduling.

Since the UE does not recognize the actual transmission mode or theactual transmission rank, a natural question is how to schedule a UE inlow-rank MU-MIMO transmission mode (for example, Rank-1 or Rank-2) whenthe UE reports a high rank PMI/CQI (for example, Ranks 3 to 8). Onepossible solution is to extract the first two columns of the high rankPMI (for example, any of Rank-3 to Rank-8 PMIs) fed back from the UE forMU-MIMO scheduling. However, such “truncated PMI” are sometimes not usedas the optimal rank-1/2 PMI computed under low rank (for example, Rank-1or Rank-2) hypothesis. Of course, although the truncated PMI mayadversely impact MU-MIMO performance, it is possible to use thesub-optimal “truncated PMI”. In addition, due to the low mobility setup(i.e., low rank adaptation) typically seen in a scenario suitable forthe MU-MIMO transmission mode, once a UE may report a rank-r PMI, the UEmay continue to report a Rank-r PMI for a long period without any Rank-1PMI. Hence, the benefit of the multi-rank PMI proposal is to allow theUE to supplement the optimal low-rank PMI such that sufficient CSIaccuracy for Rank-1 or Rank-2 MU-MIMO pairing is achieved. From thisperspective, multi-rank PMI enhances CSI accuracy in addition tofacilitating dynamic SU-MIMO and MU-MIMO switching.

Precoder for 8 Tx Antennas

In the system (e.g., 3GPP LTE Release-10 system) for supporting theextended antenna structure, for example, MIMO transmission based on 8 Txantennas may be carried out, such that it is necessary to design acodebook for supporting MIMO transmission.

In order to report a CQI of a channel transmitted through 8 antennaports, the use of codebooks shown in Tables 11 to 18 may be considered.8 CSI antenna ports may be represented by indexes of antenna ports15˜22. Table 11 shows an example of the codebook for 1-layer CSIreporting using antenna ports 15 to 22. Table 12 shows an example of thecodebook for 2-layer CSI reporting using antenna ports 15 to 22. Table13 shows an example of the codebook for 3-layer CSI reporting usingantenna ports 15 to 22. Table 14 shows an example of the codebook for4-layer CSI reporting using antenna ports 15 to 22. Table 15 shows anexample of the codebook for 5-layer CSI reporting using antenna ports 15to 22. Table 16 shows an example of the codebook for 6-layer CSIreporting using antenna ports 15 to 22. Table 17 shows an example of thecodebook for 7-layer CSI reporting using antenna ports 15 to 22. Table18 shows an example of the codebook for 8-layer CSI reporting usingantenna ports 15 to 22.

In Tables 11 to 18, φ_(n) and v_(m) can be represented by the followingequation 17.φ_(n) =e ^(jπn/2)v _(m)=[1e ^(j2πn/2) e ^(j4πn/32) e ^(j6πn/32)]^(T)  [Equation 17]

TABLE 11 i₂ i₁ 0 1 2 3 4 5 6 7 0-15 W_(2i) ₁ _(,0) ⁽¹⁾ W_(2i) ₁ _(,1)⁽¹⁾ W_(2i) ₁ _(,2) ⁽¹⁾ W_(2i) ₁ _(,3) ⁽¹⁾ W_(2i) ₁ _(+1,0) ⁽¹⁾ W_(2i) ₁_(+1,1) ⁽¹⁾ W_(2i) ₁ _(+1,2) ⁽¹⁾ W_(2i) ₁ _(+1,3) ⁽¹⁾ i₂ i₁ 8 9 10 11 1213 14 15 0-15 W_(2i) ₁ _(+2,0) ⁽¹⁾ W_(2i) ₁ _(+2,1) ⁽¹⁾ W_(2i) ₁ _(+2,2)⁽¹⁾ W_(2i) ₁ _(+2,3) ⁽¹⁾ W_(2i) ₁ _(+3,0) ⁽¹⁾ W_(2i) ₁ _(+3,1) ⁽¹⁾W_(2i) ₁ _(+3,2) ⁽¹⁾ W_(2i) ₁ _(+3,3) ⁽¹⁾ where$W_{m,n}^{(1)} = {\frac{1}{\sqrt{8}}\begin{bmatrix}v_{m} \\{\varphi_{n}v_{m}}\end{bmatrix}}$

TABLE 12 i₂ i₁ 0 1 2 3 0-15 W_(2i) ₁ _(,2i) ₁ _(,0) ⁽²⁾ W_(2i) ₁ _(,2i)₁ _(,1) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+1,0) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+1,1)⁽²⁾ i₂ i₁ 4 5 6 7 0-15 W_(2i) ₁ _(+2,2i) ₁ _(+2,0) ⁽²⁾ W_(2i) ₁ _(+2,2)_(i1) _(+2,1) ⁽²⁾ W_(2i) ₁ _(+3,2i) ₁ _(+3,0) ⁽²⁾ W_(2i) ₁ _(+3,2i) ₁_(+3,1) ⁽²⁾ i₂ i₁ 8 9 10 11 0-15 W_(2i) ₁ _(,2i) ₁ _(+1,0) ⁽²⁾ W_(2i) ₁_(,2i) ₁ _(+1,1) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+2,0) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁_(+2,1) ⁽²⁾ i₂ i₁ 12 13 14 15 0-15 W_(2i) ₁ _(,2i) ₁ _(+3,0) ⁽²⁾ W_(2i)₁ _(,2i) ₁ _(+3,1) ⁽²⁾ W_(2i) ₁ _(+1,2i) ₁ _(+3,0) ⁽²⁾ W_(2i) ₁ _(+1,2i)₁ _(+3,1) ⁽²⁾ where$W_{m,m^{\prime},n}^{(2)} = {\frac{1}{4}\begin{bmatrix}v_{m} & v_{m^{\prime}} \\{\varphi_{n}v_{m}} & {{- \varphi_{n}}v_{m^{\prime}}}\end{bmatrix}}$

TABLE 13 i₂ i₁ 0 1 2 3 0-3 W_(8i) ₁ _(,8i) ₁ _(,8i) ₁ ₊₈ ⁽³⁾ W_(8i) ₁_(+8,8i) ₁ _(,8i) ₁ ₊₈ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(,8i) ₁ _(+8,8i) ₁₊₈ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+8,8i) ₁ _(,8i) ₁ ⁽³⁾ i₂ i₁ 4 5 6 7 0-3W_(8i) ₁ _(+2,8i) ₁ _(+2,4i) ₁ ₊₁₀ ⁽³⁾ W_(8i) ₁ _(+10,8i) ₁ _(+2,8i) ₁₊₁₀ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+2,8i) ₁ _(+10,8i) ₁ ₊₁₀ ⁽³⁾ {tildeover (W)}_(8i) ₁ _(+10,8i) ₁ _(+2,8i) ₁ ₊₂ ⁽³⁾ i₂ i₁ 8 9 10 11 0-3W_(8i) ₁ _(+4,8i) ₁ _(+4,8i) ₁ ₊₁₂ ⁽³⁾ W_(8i) ₁ _(+12,8i) ₁ _(+4,8i) ₁₊₁₂ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+4,8i) ₁ _(+12,8i) ₁ ₊₁₂ ⁽³⁾ {tildeover (W)}_(8i) ₁ _(+12,8i) ₁ _(+4,8i) ₁ ₊₄ ⁽³⁾ i₂ i₁ 12 13 14 15 0-3W_(8i) ₁ _(+6,8i) ₁ _(+6,8i) ₁ ₊₁₄ ⁽³⁾ W_(8i) ₁ _(+14,8i) ₁ _(+6,8i) ₁₊₁₄ ⁽³⁾ {tilde over (W)}_(8i) ₁ _(+6,8i) ₁ _(+14,8i) ₁ ₊₁₄ ⁽³⁾ {tildeover (W)}_(8i) ₁ _(+14,8i) ₁ _(+6,8i) ₁ ₊₆ ⁽³⁾ where${W_{m,m^{\prime},m^{''}}^{(3)} = {\frac{1}{\sqrt{24}}\begin{bmatrix}v_{m} & v_{m^{\prime}} & v_{m^{''}} \\v_{m} & {- v_{m^{\prime}}} & {- v_{m^{''}}}\end{bmatrix}}},$${\overset{\sim}{W}}_{m,m^{\prime},m^{''}}^{(3)} = {\frac{1}{\sqrt{24}}\begin{bmatrix}v_{m} & v_{m^{\prime}} & v_{m^{''}} \\v_{m} & v_{m^{\prime}} & {- v_{m^{''}}}\end{bmatrix}}$

TABLE 14 i₂ i₁ 0 1 2 3 0-3 W_(8i) ₁ _(,8i) ₁ _(+8,0) ⁽⁴⁾ W_(8i) ₁ _(,8i)₁ _(+8,1) ⁽⁴⁾ W_(8i) ₁ _(+2,8i) ₁ _(+10,0) ⁽⁴⁾ W_(8i) ₁ _(+2,8i) ₁_(+10,1) ⁽⁴⁾ i₂ i₁ 4 5 6 7 0-3 W_(8i) ₁ _(+4,8i) ₁ _(+12,0) ⁽⁴⁾ W_(8i) ₁_(+4,8i) ₁ _(+12,1) ⁽⁴⁾ W_(8i) ₁ _(+6,8i) ₁ _(+14,0) ⁽⁴⁾ W_(8i) ₁_(+6,8i) ₁ _(+14,1) ⁽⁴⁾ where$W_{m,m^{\prime},n}^{(4)} = {\frac{1}{\sqrt{32}}\begin{bmatrix}v_{m} & v_{m^{\prime}} & v_{m} & v_{m^{\prime}} \\{\varphi_{n}v_{m}} & {\varphi_{m}v_{m^{\prime}}} & {{- \varphi_{n}}v_{m}} & {{- \varphi_{n}}v_{m^{\prime}}}\end{bmatrix}}$

TABLE 15 i₂ i₁ 0 0-3$W_{i_{1}}^{(5)} = {\frac{1}{\sqrt{40}}\begin{bmatrix}v_{2i_{1}} & v_{2i_{1}} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 16} \\v_{2i_{1}} & {- v_{2i_{1}}} & v_{{2i_{1}} + 8} & {- v_{{2i_{1}} + 8}} & v_{{2i_{1}} + 16}\end{bmatrix}}$

TABLE 16 i₂ i₁ 0 0-3$W_{i_{1}}^{(6)} = {\frac{1}{\sqrt{48}}\begin{bmatrix}v_{2i_{1}} & v_{2i_{1}} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 16} & v_{{2i_{1}} + 16} \\v_{2i_{1}} & {- v_{2i_{1}}} & v_{{2i_{1}} + 8} & {- v_{{2i_{1}} + 8}} & v_{{2i_{1}} + 16} & {- v_{{2i_{1}} + 16}}\end{bmatrix}}$

TABLE 17 i₂ i₁ 0 0-3$W_{i_{1}}^{(7)} = {\frac{1}{\sqrt{56}}\begin{bmatrix}v_{2i_{1}} & v_{2i_{1}} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 16} & v_{{2i_{1}} + 16} & v_{{2i_{1}} + 24} \\v_{2i_{1}} & {- v_{2i_{1}}} & v_{{2i_{1}} + 8} & {- v_{{2i_{1}} + 8}} & v_{{2i_{1}} + 16} & {- v_{{2i_{1}} + 16}} & v_{{2i_{1}} + 24}\end{bmatrix}}$

TABLE 18 i₂ i₁ 0 0 $W_{i_{1}}^{(8)} = {\frac{1}{8}\begin{bmatrix}v_{2i_{1}} & v_{2i_{1}} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 8} & v_{{2i_{1}} + 16} & v_{{2i_{1}} + 16} & v_{{2i_{1}} + 24} & v_{{2i_{1}} + 24} \\v_{2i_{1}} & {- v_{2i_{1}}} & v_{{2i_{1}} + 8} & {- v_{{2i_{1}} + 8}} & v_{{2i_{1}} + 16} & {- v_{{2i_{1}} + 16}} & v_{{2i_{1}} + 24} & {- v_{{2i_{1}} + 24}}\end{bmatrix}}$

DCI Format 0

DCI format 0 is used for the PUSCH scheduling. Control informationtransmitted by the DCI format 0 will hereinafter be described in detail.

A ‘Flag for format 0/format 1A differentiation’ field assigned to onebit is used to differentiate between DCI format 0 and DCI format 1A. DCIformat 1A is used to schedule downlink (DL) transmission and has thesame payload size as that of DCI format 0, such that there is needed afield for allowing the same format to be assigned to DCI format 0 andDCI format 1A in such a manner that DCI format 0 and DCI format 1A canbe distinguished from each other. If the ‘Flag for format 0/format 1Adifferentiation’ field is set to 0, this indicates DCI format 0. If the‘Flag for format 0/format 1A differentiation’ field is set to 1, thisindicates DCI format 1A.

A ‘Frequency hopping flag’ field is given by one bit and indicatesapplication or non-application of PUSCH frequency hopping. If the‘Frequency hopping flag’ field is set to 0, this means thenon-application of PUSCH frequency hopping. If the ‘Frequency hoppingflag’ field is set to 1, this indicates application of PUSCH frequencyhopping.

A ‘Resource block assignment and hopping resource allocation’ fieldindicates resource block allocation information in a UL subframeaccording to the presence or absence of PUSCH frequency hopping. The‘Resource block assignment and hopping resource allocation’ field iscomprised of ┌log₂ (N_(RB) ^(UL)(N_(RB) ^(UL)+1)/2)┐ bits. N_(RB) ^(UL)is a UL bandwidth configuration value, and is represented by the numberof resource blocks (RBs). In case of the application of PUSCH hopping,N_(UL) _(—) _(hop) Most Significant Bits (MSBs) are used to obtain thevalue of ñ_(PRB)(i) (physical resource block index), and (┌log₂ (N_(RB)^(UL)(N_(RB) ^(UL)+1)/2)┐−N_(UL) _(—) _(hop)) bits provide resourceallocation of the first slot in the UL subframe. In this case, N_(UL)_(—) _(hop) indicates hopping information of 1 or 2 bits according tosystem bandwidth. On the other hand, in case of non-application of PUSCHhopping, (┌log₂ (N_(RB) ^(UL)(N_(RB) ^(UL)+1)/2)┐) bits provide resourceallocation of a UL subframe.

A ‘Modulation and coding scheme and redundancy version’ field is givenby 5 bits, and indicates a PUSCH modulation order and a PUSCH redundancyversion (RV). In case of retransmission, RV indicates information as towhich subpacket is retransmitted. 0^(th) to 28^(th) states from among 32states each denoted by 5 bits are used to indicate the modulation order,and 29^(th) to 31^(th) states may indicate RV indexes (1, 2, and 3).

A ‘New data indicator’ field is given by one bit, and indicates ULscheduling information related to new data or retransmission. If muchmore toggling is performed as compared to previous transmission NDI,this means new data transmission. If no toggling occurs, this meansretransmission.

A ‘TPC command for scheduled PUSCH’ (Transmission Power Control (TPC)command for scheduled PUSCH) field is given by 2 bits, and indicates aspecific value capable of determining PUSCH transmission power.

A ‘Cyclic shift for DMRS’ field is given by 3 bits and indicates acyclic shift value used to generate a sequence for a DemodulationReference Signal (DMRS). DMRS is a reference signal (RS) to estimate aUL channel either for each antenna port or for each layer.

A ‘UL index (for TDD)’ [UL index (in case of TDD)] field is given by 2bits, and may indicate a subframe index, etc. for UL transmission in aspecific UL-DL configuration when a radio frame is configured by a TDDscheme.

A ‘Downlink Assignment Index (for TDD)’ [DL index (in case of TDD)]field is given by 2 bits, and may indicate a total number of subframesfor PDSCH transmission in a specific UL-DL configuration in a radioframe configured by a TDD scheme.

A ‘CQI request’ field is given by one 2 bit, and can a periodicallyreport a Channel Quality Information (CQI), a Precoding Matrix Indicator(PMI) and a Rank Indicator (RI) over a PUSCH.

If the ‘CQI request’ field is set to 1, a UE a periodically transmitsthe CQI, PMI, and RI reporting information over a PUSCH.

A ‘Modulation and coding scheme and redundancy version’ field mayperform signaling of an MCS index (I_(MCS)) that represents 32 statesusing 5 bits as shown in Table 4. If I_(MCS)=29 is signaled for29≦I_(MCS) 31, a ‘CQI request’ bit of the DCI format 0 is set to 1,transmission of 4 RBs or less (N_(pRB)≦4) is configured, a redundancyversion 1 (RV1) is indicated in PUSCH data retransmission, and amodulation order Q_(m) is set to 2 (Q_(m)=2). In other words, whentransmitting only the CQI, only QPSK may be used as the modulationscheme.

The 3GPP LTE system can transmit a maximum of 8 layers for SU-MIMO, andcan transmit signals using a maximum of 2 layers for MU-MIMO. From theviewpoint of the receiver, signals can be demodulated using the sameoperation irrespective of SU-MIMO and MU-MIMO.

The receiver provides signal transmission information (for example, CSI)to the transmitter. Generally, it is assumed that SU-MIMO transmissionis used for CSI reporting. Generally, CSI based on SU-MIMO is calculatedwithout considering intra-cell interference, such that performancedegradation may occur due to CQI mismatch on the assumption that theMU-MIMO transmission is attempted using the SU-MIMO based CSI.Therefore, in order to increase MU-MIMO transmission performance, amethod for reporting the precoder appropriate for MU-MIMO transmissioncan be considered.

If the UE informs the eNode B of a transmission rank capable ofacquiring maximum efficiency during the SU-MIMO transmission, forexample, if the Rank-8 based codebook index and CQI are calculated andreported, feedback information may be used as information appropriatefor Rank-8 transmission, however, the above-mentioned feedbackinformation may be inappropriate for MU-MIMO transmission in which UEseach having Rank-1 and Rank-2 are multiplexed and transmitted.Accordingly, not only CSI for SU-MIMO but also CSI for MU-MIMOtransmission should be reported to prevent performance deterioration.

Generally, two methods may be considered for reporting the CSI to thetransmitter by the receiver. One of the two methods is a method forreporting CSI using promised resources at a promised time, and the otheris a method for reporting CSI at a specific time upon receiving anindication message from the transmitter. As an exemplary method forreporting CSI at a promised time, a method for reporting the periodicCQI reporting information over a PUCCH in 3GPP LTE Release 8 may be used(However, if PUSCH data is transmitted at a periodic CSI report timepoint, CSI is multiplexed with data, and the multiplexed result istransmitted). As a method for reporting CSI at a specific time uponreceiving an indication message from the transmitter, the aperiodic CSIreporting request field is established in uplink transmission controlinformation contained in a downlink control channel, such that theestablished result can be reported over a PUSCH.

Embodiment 1

The present invention relates to a method for reporting CSI informationthat is capable of effectively supporting SU-MIMO and MU-MIMOtransmission in aperiodic CSI reporting reported through a PUSCH.Embodiment 1 can be largely classified into Embodiment 1-A thatsimultaneously reports a UE recommended CSI and a restricted rank CSIand Embodiment 1-B that reports one of the UE Recommended CSI and therestricted rank CSI.

Embodiment 1-A

Embodiment 1-A relates to a method for simultaneously reporting the UErecommended CSI and the restricted rank CSI.

Assuming that the rank range capable of being measured by the receiver(i.e., UE) is set to Rank-N, the receiver calculates CQIs of Rank-1 toRank-N such that it can select one rank capable of maximizing athroughput. However, assuming that the receiver selects a rank of Rank-Mor higher (for example, M=3), information of a rank less than Rank-Mneeded for MU-MIMO transmission may be additionally reported. In thiscase, if the restricted rank is configured and rank adaptation ispossible in the maximum rank, the rank indicator (RI) is requested. Ifthe restricted rank is set to a restricted rank such as Rank-1 orRank-2, only the PMI and CQI values may be reported without the rankindicator (RI).

If the UE recommended rank is set to M or less (for example, M=2), onlythe UE recommended CSI is reported. If the UE recommended rank is set toM or higher (for example, M=2), not only the UE recommended CSI but alsothe restricted rank CSI may be reported.

Embodiment 1-B

Embodiment 1-B relates to a method for reporting only one of the UErecommended CSI and the restricted rank CSI.

Provided that the rank range capable of being measured by the receiveris set to Rank-N, the receiver calculates CQIs of Rank-1 to Rank-N suchthat it can select one rank capable of maximizing throughput. However,provided that the receiver selects a rank of Rank-M or higher (forexample, M=3), the transmitter may request a CQI (for example, CSI ofRank of M or less) needed for MU-MIMO transmission. The transmitter mayrequest information of a rank lower than the rank range capable of beingcalculated and reported by the receiver. For this operation, a varietyof embodiments of the present invention will hereinafter be described indetail.

Embodiment 1-B-1

There may be used an indication method in which an indicator is definedin a DCI format of a PDCCH so that rank information desired by the eNodeB can be reported.

An indicator for indicating CQI attributes is defined in UL transmissioncontrol information, such that the receiver may report a CQI of a rankcontained in a range indicated by the transmitter.

A CQI request field is defined in a DCI format 0 of the 3GPP LTE Release8. If the CQI request field is set to 1, the UE transmits CSI. In thiscase, the transmitted CSI information includes a Rank, a PMI, and a CQI.Generally, rank information is selected as a UE preferred value.

For example, in a DCI format (for example, DCI format 4) newly definedfor UL transmission in a system having the extended antennaconfiguration (for example, a 3GPP LTE Release 10 system), a UEpreferred Rank is primarily reported when the eNode B (or eNB) reports aCQI. If the eNB indicates a rank, the UE may report a CQI in response toan eNB configured rank. The rank indicated by the eNB may designate aspecific rank value, may indicate a maximum rank value, may indicate anindex for the maximum rank value, may be an indicator for using thepromised rank value (or the predetermined rank value), or may be anindicator for using the promised maximum rank value.

The rank for using the eNB configured rank (or the restricted rank) maybe contained in a DCI format. For example, if the CQI request field fromamong the fields defined in the DCI format is activated, an unused fieldof the corresponding DCI format may also be interpreted as an indicatorfor using the eNB configured rank. Alternatively, the above-mentionedindicator may also be used as an indicator for using the eNB configuredrank as a combination of other fields.

For example, the bit field of the DCI format 4 may be defined asfollows.

TABLE 19 Contents Number of bit Resource block assignment N 1^(st) TBMCS and RV 5 NDI 1 2^(nd) TB MCS and RV 5 NDI 1 Precoding information MTPC command for scheduled PUSCH 2 Cyclic shift for DMRS 3 UL index (forTDD) 2 Downlink Assignment Index (for TDD) 2 CQI request 1 Aperiodic SRSrequest 1

In Table 19, if the CQI request field is activated, the MCS and RVfields for a 2^(nd) transport block (TB) may be unused. In this case,the MCS and RV fields for the 2^(nd) TB may be used to indicate the eNBconfigured rank (or restricted rank).

Embodiment 1-B-2

A method for establishing the report rank range according to PDCCH DCIformat types may be used.

Control information for UL transmission may be classified into a DCIformat for supporting single layer transmission and a DCI format forsupporting multi-layer transmission. For example, single antennatransmission is single layer transmission. For this operation, DCIformat 0 is defined. In addition, in order to support a specificallocation method in spite of single layer transmission, a new DCIformat 0A (for example, DCI format 0A) may be defined. In spite ofsingle layer transmission, a new DCI format (for example, DCI format 0B)including a single layer precoder indicator may be defined. In addition,a DCI format for MIMO transmission may be defined, and a new DCI format(for example, DCI format 4) may be defined for multi-TB transmission.

A CQI request field may be defined in each DCI format. In this case, ifthe CQI request field of the DCI format supporting one transport block(TB) is activated, the UE calculates and reports a CQI in the restrictedrank. In addition, if the CQI request field of the DCI format supportingmultiple transport blocks is activated, the UE calculates and reports aCQI in a rank that can be measured and received by the UE.

In other words, if the CQI request indication is received from the DCIformat supporting the single TB in the same manner as in the DCI format‘0’, ‘0A’, or ‘0B’, a CQI is calculated in the restricted rank. If theCQI request indication is received from a DCI format supporting multipleTBs in the same manner as in the DCI format ‘4’, the UE calculates andreports the CQI at a rank that can be measured and received by the UE.

In this case, the restricted rank may be established as a valueindependent of the UE measurable rank. The restricted rank may beinformed through the RRC signaling or may be set to a fixed value. Forexample, the restricted rank may be set to a maximum of Rank 2.

Embodiment 1-B-3

A method for establishing a reported information type according to anumber of transmission PUSCH may be used.

When a CQI request field of the DCI format 0 is set to 1 in the 3GPP LTERelease-8, PUSCH is transmitted at a (n+k)-th time point correspondingto k subframes from a time at which a DCI is received over a PDCCH. Incase of FDD, k is set to 4 (k=4).

The reported CSI may be changed according to whether ‘n’ is an even orodd number on the basis of the n-th subframe at which a DCI formathaving an activated CQI request field requesting the aperiodic CQI isreceived. For example, if the n-th subframe is an even subframe, CSI ofthe UE recommended rank may be reported. Additionally, if the n-thsubframe is an odd number, CSI of the restricted rank may be reported.Alternatively, if the n-th subframe is an odd subframe, CSI of the UErecommended rank is reported. Additionally, if the n-th subframe is aneven number, CSI of the restricted rank may be reported.

At the n-subframe corresponding to a reception time of the DCI format inwhich a CQI request field requesting the aperiodic CQI is requested isactivated, the reported CSI may be changed according to whether thevalue of (n+k) is an even or odd number. For example, if the (n+k)^(th)subframe is an even subframe, CSI of the UE recommended rank may bereported. Additionally, if the (n+k)^(th) subframe is an odd number, CSIof the restricted rank may be reported. Alternatively, if the (n+k)^(th)subframe is an odd subframe, CSI of the UE recommended rank may bereported. Additionally, if the (n+k)^(th) subframe is an odd subframe,CSI of the restricted rank may be reported.

The CSI reporting method for effectively supporting the SU-MIMO andMU-MIMO transmission proposed in Embodiment 1 may be applied to atransmission mode newly defined in a system (for example, 3GPP LTE-A)supporting the extended antenna configuration.

Embodiment 2

A method for selecting a precoder suitable for the restricted rank usingthe precoder selected in response to the UE recommended rank on thecondition that the UE recommended rank is higher than the restrictedrank will hereinafter be described.

The precoder having Rank-N is composed of a combination of N precodingvectors. A low rank may be transmitted using some vectors from among Nvectors. Using some vectors of the precoder may be referred to as subsetselection.

A variety of methods for performing subset selection for the precoderthat is reported from the UE to the eNB may be used. For example, 1) amethod for selecting arbitrary vectors at random, 2) a method forselecting a subset according to a predetermined or promised rule, and 3)a method for reporting a vector preferred by the reporting side (i.e.,UE) may be used. In this case, the above-mentioned methods (1) (Methodfor selecting arbitrary vectors) and (2) (Method for selecting a subsetaccording to a promised rule) need not use additional signals. On theother hand, according to the method (3) for reporting the UE preferredvector, the reporting side (IE) has to provide subset selectioninformation to the reported side (eNB).

Rules and examples applicable to the above-mentioned method (2) forselecting a subset according to the promised rule will hereinafter bedescribed.

For example, a specific rule for sequentially selecting columns startingfrom the first column of the precoder may be used. In case of Rank-1, afirst column may be selected. In case of Rank-2, first and secondcolumns may be selected.

In another example, another rule for selecting a subset in considerationof a layer mapped to a transport block (TB) may be used. A precodercorresponding to the M^(th) layer from among layers mapped to the TB maybe selected. For example, assuming that 2 TBs (TB1 and TB2) are mappedto 4 layers (Layer 1, Layer 2, Layer 3, Layer 4), the 1^(st) TB (TB1) ismapped to the 1^(st) and 2^(nd) layers (Layer 1 and Layer 2), and the2^(nd) TB (TB2) is mapped to the 3^(rd) and 4^(th) layers. In this case,if M=1 is given in precoder subset selection, a subset corresponding toa first layer (Layer 1) mapped to a TB1 and a subset corresponding to afirst layer (Layer 3) mapped to a TB2 may be selected as two precoders.

Exemplary signaling methods capable of being applied to the method forreporting the preferred vector at the reporting side will hereinafter bedescribed in detail.

For example, the precoder subset may be reported as a bitmap format. Incase of a Rank-N, by means of a bitmap composed of N bits for displayingN vectors, information as to what the UE preferred precoder vector iscan be reported to the eNB.

In another example, provided that preferring one vector from among theprecoder subsets is reported, information as to which one of theprecoder vectors is preferred by the UE may be reported to the eNB usinglog₂(N) bits (where N=Rank).

If the precoder is selected according to the above-mentioned schemes, aCQI corresponding to the selected precoder may be calculated andreported. For SU-MIMO transmission, the Rank-N precoder may be selected,and a CQI may be calculated in response to the selected precoder. Inthis case, some precoder vectors are selected from among the Rank-Nprecoder, a CQI corresponding to the selected subset may bere-calculated. For example, if the precoder for a Rank-4 is selected, aCQI for Rank-4 may be calculated by the precoder. In addition, if twoprecoder vectors are selected on the basis of the Rank-4 precoder, aRank-2 CQI may be calculated.

A variety of exemplary feedback methods applicable to theabove-mentioned precoder selection will hereinafter be described indetail.

According to a first feedback method, a method for feeding back“RI-PMI1-CQI1-PMI2-CQI2” may be used. In the first feedback method, RIis rank information corresponding to PMI1 (or Precoder1), and CQI1 iscalculated on the basis of PMI1. PMI1 is precoder(s) selected from amongthe PMI1, and CQI2 is calculated on the basis of the PMI2. In this case,each of PMI1, PMI2, CQI1 and CQI2 may be transmitted one or more times.

According to a second feedback method, a method for feeding back“RI-PMI1-CQI1-CQI2” may be used. In the second feedback method, RI isrank information corresponding to PMI1 (or Precoder1), and CQI1 iscalculated on the basis of PMI1. CQI2 may be calculated on the basis ofPMI2 (or Precoder2). PMI2 is precoder(s) selected from among the PMI1.If PMI2 is selected by the promised rule, PMI2 is not reported. In thisway, each of PMI1, CQI1, and CQI2 may be transmitted one or more times.

According to a third feedback method, a method for feeding back“RI-PMI1-CQI1-PSI (Precoder Selection Indicator)-CQI2” may be used. Inthe third feedback method, RI is rank information corresponding to PMI1(or Precoder1), and CQI1 is calculated on the basis of PMI1. PMI2 (orPrecoder2) is precoder(s) selected from among the PMI1, and may report aPSI to indicate which value was selected as the PMI2. In this case, eachof PMI1, CQI1, and CQI2 may be transmitted one or more times.

In case of the application of the above-mentioned feedback methods,feedback information may be simultaneously reported according to thereported channel (e.g., PUSCH or PUCCH), or may be reported at differentcycles. For example, in case of feedback reporting over a PUSCH, an RI,a PMI and a CQI may be reported over one channel. If a PMI2 selected assome subsets of the PMI1 is reported, PMI2 and CQI2 may besimultaneously reported over only one channel. Alternatively, in case ofthe feedback reporting over a PUCCH, RI, PMI and CQI may be reported atdifferent cycles. If a PMI2 selected as some subsets of a PMI1 isreported as described above, PMI2 and CQI2 may also be reported atdifferent cycles.

Embodiment 3

A method for determining a transmission time point of feedbackinformation when precoder information for the restricted rank istransmitted will hereinafter be described in detail.

Generally, a low rank precoder is used from the viewpoint of one user toimplement MU-MIMO transmission, and it is preferable that users havinglow spatial correlation be generally multiplexed and transmitted. Evenin the case of MU-MIMO transmission, the UE assumes SU-MIMO withoutdistinction between MU-MIMO transmission and SU-MIMO transmission, andthen determines and reports a rank value at which the maximum throughputis expected. Under the condition that the UE recommended rank and theprecoder in response to the corresponding rank are selected andreported, a high rank precoder and associated CQI may be calculated andreported. When the high rank precoder is reported, a low rank precodermay be configured for MU-MIMO transmission using a subset of thereported precoder, or a method for additionally reporting the low rankprecoder may be used.

First, the method for allowing an eNB to select a precoder subsetreported from the UE so as to perform MU-MIMO transmission willhereinafter be described in detail. If the precoder subset depending onthe UE recommended rank is used for MU-MIMO transmission, a CQI isneeded for the MU-MIMO transmission of the eNB. Since the eNB receivesreport information of a CQI calculated on the basis of the precoder ofthe UE recommended rank, this CQI may be used as a MU-MIMO CQI. However,a channel state of the CQI calculated on the basis of the UE recommendedrank precoder may be different from a channel state requisite for datathat is transmitted using the corresponding precoder subset.Accordingly, in the case in which the eNB uses the CQI calculated on thebasis of the UE recommended rank precoder as the MU-MIMO CQI, a CQImismatch may occur. Preferably, it is preferable that the CQI calculatedbased on the precoder subset be reported to improve a MU-MIMOthroughput.

Second, the method for allowing a UE to additionally report the low rankprecoder will hereinafter be described. When the low rank precoder isreported, the CQI calculated on the basis of the precoder is preferablyreported simultaneously with the low rank precoder.

PUCCH resources allocated from the eNB to the UE so as to report channelinformation using the conventional scheme are limited, and the precoderof the UE recommended rank and associated CQI may be reported over aPUCCH. Accordingly, in order to report the precoder subset andassociated CQI or in order to report the restricted rank precoder andassociated CQI, there is needed a method for newly defining a reporttime point and/or resources of such additional feedback information.

Embodiment 3-A

A method for establishing an offset at which the restricted rank basedprecoder and CQI is reported will hereinafter be described in detail.

In case of periodic PUCCH feedback reporting, a time point for RI andPMI/CQI transmission is defined. Generally, rank and PMI/CQI informationare reported at different subframes. Specifically, RI is reported at acycle longer than that of the PMI/CQI. If a rank is reported, thePMI/CQI information corresponding to the previously reported rank isreported in response to the corresponding transmission cycle untilreaching the next rank reporting time.

If a higher rank is reported as described above, it is necessary toreport the low rank PMI and associated CQI or the subset of a higherrank precoder and associated CQI. The low-rank precoder/CQI informationmay be referred to as PMI/CQI information of the restricted rank.

The time point at which the restricted rank PMI/CQI is reported may besome parts of another timing at which the higher rank PMI/CQI isreported. That is, a specific time from among a high-rank PMI/CQI reporttiming between rank reporting periods may be considered a report timingof the restricted rank PMI/CQI. The restricted rank PMI/CQI may bereported at a cycle longer than the reporting timing of the UErecommended rank PMI/CQI (that is, the restricted rank PMI/CQI may bereported less frequently than the UE recommended rank PMI/CQI), and maybe reported with a predetermined offset at a UE recommended rank PMI/CQIreporting time point. Especially, an offset of the restricted rankPMI/CQI transmission time point may be reported later than the UErecommended rank PMI/CQI transmission time point.

On the other hand, a timing offset of a subsframe for rank informationtransmission may be the same subframe on the basis of the UE recommendedrank PMI/CQI subframe, or may be transmitted at a subframe locatedbefore the above-mentioned subframe. In order to prevent the restrictedrank PMI/CQI transmission from colliding with a subframe at which rankinformation is transmitted (i.e., in order to prevent the restrictedrank PMI/CQI from being transmitted at the same subframe as the rankinformation), the restricted rank PMI/CQI may be reported later than areference subframe at which the UE recommended rank PMI/CQI istransmitted. In addition, the offset for a transmission time point ofthe restricted rank PMI/CQI may be set to a positive (or negative)integer excluding ‘0’.

FIGS. 22 and 23 illustrate examples of the restricted rank PMI/CQItransmission timing and offset.

Examples of the restricted rank PMI/CQI transmission timing and offsetwill hereinafter be described with reference to FIGS. 22 and 23. InFIGS. 22 and 23, N_(s) is a slot index, and may be 0, 1, . . . , Ns.That is, one radio frame composed of 10 subframes is shown in FIGS. 22and 23, and └N_(s)/2┘ is a subframe index.

In FIG. 22, a CQI/PMI based on the UE recommended rank is transmitted atintervals of Np, RI is transmitted at intervals of an integer multiple(Np×M_(RI)) of the CQI/PMI cycle based on the UE recommended rank, andRI is transmitted at a time point located ahead of the CQI/PMItransmission time point of the UE recommended rank by a predeterminedoffset (N_(offset,RI)). As previously stated in the above-mentionedembodiments, the restricted rank PMI/CQI may be transmitted at a timepoint located behind a CQI/PMI transmission time point of the UErecommended rank by a predetermined offset (N_(offset,CQI)), and may betransmitted with a cycle longer than the UE recommended rank CQI/PMItransmission cycle.

As can be seen from FIG. 23, a WB CQI/PMI and an SB CQI are transmittedas the UE recommended rank CQI/PMI. WB CQI/PMI and SB CQI may bealternately transmitted at intervals of Np, and the transmission cycleof the WB CQI/PMI may be set to (H×Np). RI may be transmitted atintervals of an integer multiple of the WB CQI/PMI cycle of the UErecommended rank (i.e., at intervals of (H×Np×M_(RI))). RI istransmitted at a time point located ahead of a CQI/PMI transmission timepoint of the UE recommended rank by a predetermined offset(N_(offset,RI)). As previously sated in the above-mentioned embodiments,the restricted rank PMI/CQI may be transmitted at a time point locatedbehind a CQI/PMI transmission time point of the UE recommended rank by apredetermined offset (N_(offset,CQI)), and may be transmitted with acycle longer than the UE recommended rank CQI/PMI transmission cycle.

Embodiment 3-A-1

An example of a feedback mode of the restricted rank PMI/CQI willhereinafter be described in detail.

In accordance with Embodiment 3-A-1, a feedback mode of the restrictedrank PMI/CQI may be based on a feedback mode of the UE recommended rankPMI/CQI. For example, if the feedback mode of the UE recommended rankPMI/CQI is a mode for transmitting a WB PMI and a WB CQI, the restrictedrank PMI/CQI may also be transmitted as the WB PMI and WB CQI.Alternatively, if the feedback mode of the UE recommended rank PMI/CQIis a mode for transmitting the WB PMI and SB CQI, the restricted rankPMI/CQI may also be transmitted as the WB PMI and SB CQI.

In addition, if the SB CQI is reported in the same manner as in bandcycling, there may be used one cycle in which a WB CQI is reported andall SB CQIs for individual bandwidth parts (BPs) are reported. Therestricted rank PMI/CQI may be reported during one cycle in which a WBCQI and SB CQIs of individual BPs are reported. That is, at least onecycle from among the band cyclic reporting period having one or moreperiods in the RI report cycle may be set to the report period of therestricted rank PMI/CQI.

An example of the restricted rank PMI/CQI reporting period willhereinafter be described with reference to FIG. 24. In FIG. 24, one ofthe band cyclic reporting periods, each of which is used to report a WBCQI and a CQI of each BP, from among the RI reporting period(H×Np×M_(RI)) may correspond to └Ns/2┘ of 1˜4. In FIG. 24, as previouslystated in the above-mentioned embodiments, the restricted rank PMI/CQImay be transmitted in one of the band cyclic reporting periods.

Embodiment 3-A-2

Another example of a feedback mode of the restricted rank PMI/CQI willhereinafter be described in detail.

In accordance with Embodiment 3-A-2, a feedback mode of the restrictedrank PMI/CQI is established to have a constant feedback modeirrespective of the feedback mode of the UE recommended rank PMI/CQI.For example, the restricted rank PMI/CQI may be established to have a WBPMI and a WB CQI.

Embodiment 3-B-1

Embodiment 3-B-1 relates to a feedback method on the condition that amultiple-granular precoder is defined. The multiple-granular precodermay be comprised of a combination of two codebooks (W1 and W2). W1 andW2 may be composed of various codebooks. Therefore, the eNB may receivereport information of different feedback indicators (W1 and W2) of theprecoder and then select the entire precoder. Different information (W1and W2) for the precoder may be reported at different time points. Forexample, W1 may be reported at long term and W2 may be reported at shortterm. When W1 is reported at long term, W1 may be reported along withrank information. Alternatively, W1 and W1 may be simultaneouslyreported. That is, in case of using the multiple-granular precoder, atransmission time point of feedback information may be established asshown in the following table 20.

TABLE 20 T1 T2 Mode (1) Rank + W1 (wideband) W2 (wideband) + CQI(wideband) Mode (2) Rank W1 (wideband) + W2 (wideband) + CQI (wideband)

As can be seen from Mode (1) of Table 20, rank information (RI) and a WBW1 may be transmitted at the same time point (T1), and a WB W2 and a WBCQI may be transmitted at an arbitrary time T2 lagging the T1 time.Alternatively, as can be seen from Mode (2), rank information (Ri) maybe transmitted at the time T1, and a WB W1, a WB W2 and a WB CQI may betransmitted at an arbitrary time T2 lagging the T1 time.

In this way, under the condition that the indicators (W1 and W1) for theprecoder are reported at the same or different time points, therestricted rank PMI/CQI may be fed back. If the restricted rank PMI/CQIis reported, W1 and W2 suitable for the restricted rank may be selectedand fed back. In addition, a CQI calculated on the basis of the selectedW1 and W2 may be fed back. In this case, W1, W2 and CQI may be reportedat the same time point (i.e., at one subframe).

A feedback method including the restricted rank PMI/CQI under themultiple-granular precoder will hereinafter be described with referenceto FIGS. 25 and 26.

In FIG. 25, RI and PMI1 (i.e., WB W1) are simultaneously transmitted atone time point, and WB PMI2 (i.e., WB W2) and WB CQI are transmitted ata later time point. In this case, PMI1, PMI2, and CQI may be feedbackinformation that is selected and calculated according to the UErecommended rank. In addition, the restricted rank PMI/CQI may betransmitted at a time point located behind the UE recommended rankCQI/PMI transmission time point by a predetermined offset(N_(offset,CQI)). In FIG. 25, PMI1, PMI2, and CQI of the restricted rankare transmitted at a time point corresponding to └Ns/2┘=2.

In FIG. 26, after RI is transmitted, WB PMI1 (i.e. WB W1), WB PMI2(i.e., WB W2) and WB CQI are simultaneously transmitted. In this case,the transmitted PMI1, PMI2, and CQI may be feedback information that isselected and calculated according to the UE recommended rank. Inaddition, the restricted rank PMI/CQI may be transmitted at a time pointlocated behind the UE recommended rank CQI/PMI transmission time pointby a predetermined offset (N_(offset,CQI)). In FIG. 26, PMI1, PMI2, andCQI of the restricted rank are transmitted at a time point correspondingto └Ns/2┘=2.

Embodiment 3-B-2

Embodiment 3-B-2 relates to a feedback method on the condition that amultiple-granular precoder is defined.

If multiple-granular precoder indicators (i.e., W1 and W2) are reportedto the eNB, different feedback modes may be indicated using a PrecoderType Indication (PTI) bit.

In one feedback mode, R1, W1 and W2/CQI are transmitted at differentsubframes, and W1, W2 and CQI may be established as WB information. Inthe other feedback mode, W2 and CQI are reported at the same subframe, aW2/CQI frequency granularity may be WB or SB according to the reportedsubframe. That is, feedback modes of Table 21 can be defined.

TABLE 21 T1 T2 T3 Mode (1) PT I(0) + Rank W1 (wideband) W2 (wideband) +CQI (wideband) Mode (2) PTI (1) + Rank W2 (wideband) + W2 (subband) +CQI (wideband) CQI (subband)

In Table 21, if PTI is set to zero (0), RI is transmitted at a timepoint T1, and a WB W1 is transmitted at an arbitrary time point T2.Thereafter, a feedback function may be carried out at an arbitrary timepoint T3 according to a mode for WB W2 and WB CQI transmission. In Table21, if PTI is set to 1, RI is transmitted at a time point T1, and WB W1and WB CQI are then transmitted at an arbitrary time point T2. Afterthat, a feedback function may be carried out at an arbitrary time pointT3 according to a mode for SB W2 and SB CQI transmission.

Mode (1) or Mode (2) may be determined according to a feedback cycle ofthe rank information (RI). After Mode (1) or Mode (2) is determined by aPTI, WB W1, WB W2, and WB CQI may be reported in response to a CQI cycle(See Mode (1)) or WB W2/WB CQI and SB W2/SB CQI may be reported inresponses to a CQI cycle (See Mode (2)). A reference of the reportedcycle may be set to a transmission time point of WB W2 and WB CQI.Transmission timing of other feedback information may be determined asan offset for WB W2/WB CQI transmission timing.

In the feedback method of this embodiment, a method for establishing thecycle and offset for such WB W1 feedback will hereinafter be describedin detail.

According to a first method, a WB W1 transmission cycle may beestablished at intervals of a specific time longer than a PTI/RItransmission cycle. That is, the WB W1 transmission cycle may beestablished less frequently than the PTI/RI transmission cycle. Inaddition, the WB W1 cycle may be an integer multiple of a transmissioncycle of WB W2 and WB CQI. In addition, the WB W1 transmission timingmay be established as an offset value of the reference timing (i.e., atransmission subframe of WB W2 and WB CQI).

According to a second method, the WB W1 transmission timing may beestablished as an offset value of the reference timing (i.e., atransmission subframe of WB W2 and WB CQI). In addition, if a PTI ofPTI/RI feedback information is set to a specific value (0 or 1), the WBW1 may be immediately transmitted once after the PTI/RI transmission.

In the feedback method of this embodiment, a method for feeding back therestricted rank PMI/CQI will hereinafter be described in detail. Theabove-mentioned WB W1, WB W2, WB CQI, SB W2 and SB CQI are used asfeedback information that is selected and calculated according to the UErecommended rank, and the restricted rank PMI/CQI may be furthertransmitted.

If PTI reported along with RI is set to 0, WB PMI and WB CQI may bereported as the restricted rank PMI/CQI. WB W1, WB W2 and WB CQI of therestricted rank may be reported at the same time point. In somesubframes from among subframes in which (WB W2+WB CQI) of the UErecommended rank is reported, WB W 1, WB W2 and WB CQI of the restrictedrank may be simultaneously reported.

Alternatively, if PTI reported along with RI is set to 1, the restrictedrank PMI/CQI may be reported. In this case, the following two methodsmay be used to report the restricted rank PMI/CQI.

In the first method, only WB W1, WB W2 and WB CQI of the restricted rankmay be reported as the restricted rank PMI/CQI.

In the second method, WB W1, WB W2 and WB CQI of the restricted rank maybe reported at one subframe, and SB W1 and SB CQI of the restricted rankmay be reported at a different subframe. Transmission time points of theabove-mentioned factors may be established according to the band cyclicreporting period.

Embodiment 4

Embodiment 4 discloses a method for deciding the number of bits ofdifferent precoder indexes constructing the entire precoder.

Tables 11 to 18 show codebooks for enabling a BS (or eNB) having 8 Txantennas in the 3GPP LTE system to report a CSI. The CSI reportingcodebooks shown in Tables 11 to 18 may decide the codebook elementaccording to two kinds of feedback reports. Although Tables 11 to 18represent two feedback report values as i1 and i2, i1 and i2 correspondto one precoder index W1 (or PMI1) and another precoder index W2 (orPMI2), respectively. Two report values may have different time points,and may be established to have different frequency granularities. Fordata transmission, the number (# of element) of constituent elements ofthe codebook may have different values according to the number ofUE-recommended ranks, as represented by the following Table 22.

TABLE 22 Rank 1 2 3 4 5 6 7 8 # of element for i1 16 16 4 4 4 4 4 1 # ofelement for i2 16 16 16 8 1 1 1 1

In Table 22, i1 may be defined to have an element of 16, 4 or 1according to the rank, and i2 may be defined to have an element of 16, 8or 1 according to the rank. For feedback, i1 may be represented by 0 to4 bits, and i2 may be represented by 0 to 4 bits. A maximum number ofbits capable of expressing i1 and i2 according to the rank can berepresented by the following Table 23.

TABLE 23 Rank 1 2 3 4 5 6 7 8 Maximum bits for i1 4 4 2 2 2 2 2 0Maximum bits for i2 4 4 4 3 0 0 0 0

Due to limitation of control channel capacity defined to report feedbackinformation, bits capable of representing i1 and i2 for CSI reportingmay be restricted. That is, the i1 and i2 values must be transmitted toreport a CSI. If an indicator for the it value and/or an indicator forthe i2 value may be transmitted along with RI or CQI, an error ratesimilar to that of a channel that reports RI or CQI defined in thelegacy 3GPP LTE Release-8 or Release-9 may be implemented and at thesame time feedback information may be transmitted as necessary.

In the case where the indicator for the i1 value and/or the indicatorfor the i2 value are simultaneously transmitted along with RI or CQI,for example, RI may be reported through one subframe, and an indicatorfor the i1 value, an indicator for the i2 value and a CQI may besimultaneously reported through another subframe. In another example, RIand the indicator for i1 may be simultaneously reported through onesubframe, and the indicator for i2 and a CQI may be simultaneouslytransmitted through another subframe.

The legacy 3GPP LTE Release-8 or Release-9 assumes transmission of amaximum of 2 bits for the RI. In case of RI transmission through aPUCCH, the same coding method as in ACK/NACK transmission may be used.In addition, it is assumed that a maximum of 11 bits is transmitted toreport CQI/PMI, such that the coding may be carried out using aReed-Muller (RM) code that is capable of supporting a maximum of 13bits.

If it is assumed that the system (e.g., 3GPP LTE Release-10 system)supporting the extended antenna structure simultaneously reports i1, i2,and CQI (i1/i2/CQI), a maximum of 15 (=4+4+7) bits may be requisite forRank-1 or Rank-2. To transmit 15 bits, the coding method for extendingthe legacy RM code may be used, or a control signal may be reportedusing the conventional convolution code. In addition, in order toimplement the same level as that of maximum bits defined in the legacysystem, a method for reducing the size of indicator bits for i1 and i2may be used as necessary.

Table 24 shows numbers of bits needed to simultaneously report i1, i2and CQI (i1/i2/CQI). If the indicator bits for i1 and i2 are set to 0˜4,the number of bits transmitted in one subframe is shown in Table 24. Inaddition, according to the rank, the number of indicator bits for i1 ori2 may be a fullset or subset. For example, if the i1 indicator bit isset to 4 and the i2 indicator bit is set to 4, all the fullsets of acodebook may be used to transmit Rank-1 and Rank-2. Alternatively, inthe case where 2 bits are used for i1 or (W1) and 4 bits are used for i2(or W2), the subset of i1 may be used in Rank-1 or Rank-2, the fullsetof i2 may be used, and all fullsets of i1 and i2 may be used in Rank-3.In Table 24, F may represent the fullset, and S may represent thesubset. In addition, in association with each expression (F/F, F/S, S/For S/S) of Table 21, a number located in front of a specific symbol (/)represents bits for i1 and another number located behind the symbol (/)represents bits for i2.

TABLE 24 Rank R i1 i2 i1 + i2 + CQI 1 2 3 4 5 6 7 8 1/ 4 4 4 + 4 + 7 F/FF/F — — — — — — 2/ 3 4 + 3 + 7 F/S F/S — — — — — — 3 2 4 + 2 + 7 F/S F/S— — — — — — 1 4 + 1 + 7 F/S F/S — — — — — — 0 4 + 0 + 7 F/S F/S — — — —— — 3 4 3 + 4 + 7 S/F S/F — — — — — — 3 3 + 3 + 7 S/S S/S — — — — — — 23 + 2 + 7 S/S S/S — — — — — — 1 3 + 1 + 7 S/S S/S — — — — — — 0 3 + 0 +7 S/S S/S — — — — — — 2 4 2 + 4 + 7 S/F S/F F/F — — — — — 3 2 + 3 + 7S/S S/S F/S F/F — — — — 2 2 + 2 + 7 S/S S/S F/S F/S — — — — 1 2 + 1 + 7S/S S/S F/S F/S — — — — 0 2 + 0 + 7 S/S S/S F/S F/S F/F F/F F/F — 1 41 + 4 + 7 S/F S/F S/F — — — — — 3 1 + 3 + 7 S/S S/S S/F S/F — — — — 21 + 2 + 7 S/S S/S S/S S/S — — — — 1 1 + 1 + 7 S/S S/S S/S S/S — — — — 01 + 0 + 7 S/S S/S S/S S/S S/F S/F S/F — 0 0 0 + 0 + 7 S/S S/S S/S S/SS/S S/S S/S F/F

To apply the legacy coding method to PUCCH feedback transmission or toobtain an error rate similar to that of the conventional feedbackchannel, 13 bits or less may be transmitted within one subframe. In thiscase, when using a subset including only too small a number of codebookelements, the probability that the codebook element for expressing a CSIappropriate for an actual channel state is contained in thecorresponding subset is gradually decreased, resulting in a reduction intransmission throughput. Therefore, the number of feedback bits must bereduced and a subset of an appropriate level must be used.

For example, for Rank-1 and Rank-2, a maximum of 4 bits may be requestedfor each of i1 and i2. The subset of an index in which ‘(bits for the i1indicator/bits for the i2 indicator)’ is set to any of (4/3), (4/2),(3/3), (3/2), (2/3), (2/2), etc. may be used as necessary.

In addition, the fullset or subset of index may be used according torank. For example, in order to implement the level corresponding to amaximum of 11 bits, ‘2 bits/2 bits’ may be used for i1 and i2 (i1/i2).In this case, ‘2 bits/2 bits’ may be used at Ranks 1 to 4, ‘2 bits/0bit’ may be used at Ranks 5 to 7, and ‘0 bit/0 bit’ may be used atRank-8. Alternatively, in order to implement the level corresponding toa maximum of 13 bits, ‘3 bits/2 bits’ may be used for i1 and i2 (i1/i2).In this case, ‘3 bits/2 bits’ may be used at Ranks 1 and 2, ‘2 bits/4bits’ may be used at Rank-3, ‘2 bits/3 bits’ may be used at Rank-4, ‘2bits/0 bit’ may be used at Ranks 5 to 7, and ‘0 bit/0 bit’ may be usedat Rank-8. Table 25 shows exemplary bit numbers capable of being usedfor i1 and i2 (i1/i2) for each rank.

TABLE 25 Rank (i1/i2) 1 (4/2), (3/3), (3/2), (2/3), (2/2) 2 (4/2),(3/3), (3/2), (2/3), (2/2) 3 (2/4), (2/3), (2/2), (2/1), (2/0), (1/4),(1/3), (1/2), (1/1), (1/0) 4 (2/3), (2/2), (2/1), (2/0), (1/3), (1/2),(1/1) 5 (2/0) 6 (2/0) 7 (2/0) 8 (0/0)

Table 26 shows preferable combination of number of bits of i1/i2 ofTable 25.

TABLE 26 Rank i1/i2 1 2 3 4 5 6 7 8 4/2 4/2 2/4 2/3 2/0 2/0 2/0 0/0 3/33/3 2/4 2/3 2/0 2/0 2/0 0/0 3/2 3/2 2/3 2/3 2/0 2/0 2/0 0/0 2/2 2/2 2/22/2 2/0 2/0 2/0 0/0

Table 27 shows bits required either when the RI and the i1 index aresimultaneously transmitted within one subframe or when the i2 index andthe CQI are simultaneously transmitted within another subframe.

TABLE 27 Rank RI i1 i2 RI + i1 i2 + CQI 1 2 3 4 5 6 7 8 3 4 4 3 + 4 4 +7 F/F F/F — — — — — — 3 3 + 7 F/S F/S — — — — — — 2 2 + 7 F/S F/S — — —— — — 1 1 + 7 F/S F/S — — — — — — 0 0 + 7 F/S F/S — — — — — — 3 4 3 + 34 + 7 S/F S/F — — — — — — 3 3 + 7 S/S S/S — — — — — — 2 2 + 7 S/S S/S —— — — — — 1 1 + 7 S/S S/S — — — — — — 0 0 + 7 S/S S/S — — — — — — 2 43 + 2 4 + 7 S/F S/F F/F — — — — — 3 3 + 7 S/S S/S F/S F/F — — — — 2 2 +7 S/S S/S F/S F/S — — — — 1 1 + 7 S/S S/S F/S F/S — — — — 0 0 + 7 S/SS/S F/S F/S F/F F/F F/F — 1 4 3 + 1 4 + 7 S/F S/F S/F — — — — — 3 3 + 7S/S S/S S/F S/F — — — — 2 2 + 7 S/S S/S S/S S/S — — — — 1 1 + 7 S/S S/SS/S S/S — — — — 0 0 + 7 S/S S/S S/S S/S S/F S/F S/F — 0 0 3 + 0 0 + 7S/S S/S S/S S/S S/S S/S S/S F/F 2 4 4 2 + 4 4 + 7 F/F F/F — — — — — — 33 + 7 F/S F/S — — — — — — 2 2 + 7 F/S F/S — — — — — — 1 1 + 7 F/S F/S —— — — — — 0 0 + 7 F/S F/S — — — — — — 3 4 2 + 3 4 + 7 S/F S/F — — — — —— 3 3 + 7 S/S S/S — — — — — — 2 2 + 7 S/S S/S — — — — — — 1 1 + 7 S/SS/S — — — — — — 0 0 + 7 S/S S/S — — — — — — 2 4 2 + 2 4 + 7 S/F S/F F/F— — — — — 3 3 + 7 S/S S/S F/S F/F — — — — 2 2 + 7 S/S S/S F/S F/S — — —— 1 1 + 7 S/S S/S F/S F/S — — — — 0 0 + 7 S/S S/S F/S F/S — — — — 1 42 + 1 4 + 7 S/F S/F S/F — — — — — 3 3 + 7 S/S S/S S/F S/F — — — — 2 2 +7 S/S S/S S/S S/S — — — — 1 1 + 7 S/S S/S S/S S/S — — — — 0 0 + 7 S/SS/S S/S S/S — — — — 0 0 2 + 0 0 + 7 S/S S/S S/S S/S — — — — 1 4 4 1 + 44 + 7 F/F F/F — — — — — — 3 3 + 7 F/S F/S — — — — — — 2 2 + 7 F/S F/S —— — — — — 1 1 + 7 F/S F/S — — — — — — 0 0 + 7 F/S F/S — — — — — — 3 41 + 3 4 + 7 S/F S/F — — — — — — 3 3 + 7 S/S S/S — — — — — — 2 2 + 7 S/SS/S — — — — — — 1 1 + 7 S/S S/S — — — — — — 0 0 + 7 S/S S/S — — — — — —2 4 1 + 2 4 + 7 S/F S/F — — — — — — 3 3 + 7 S/S S/S — — — — — — 2 2 + 7S/S S/S — — — — — — 1 1 + 7 S/S S/S — — — — — — 0 0 + 7 S/S S/S — — — —— — 1 4 1 + 1 4 + 7 S/F S/F — — — — — — 3 3 + 7 S/S S/S — — — — — — 22 + 7 S/S S/S — — — — — — 1 1 + 7 S/S S/S — — — — — — 0 0 + 7 S/S S/S —— — — — — 0 0 1 + 0 0 + 7 S/S S/S — — — — — —

If the maximum number of Ranks reported by a UE is determined accordingto either a maximum rank capable of being received at the UE or amaximum rank to be transmitted from an eNB, a bit for Rank indicationmay be determined. Provided that RI and i1 are combined andsimultaneously transmitted, a maximum number of bits requisite forfeedback may be 7 (=3+4) bits, and a minimum number of bits may be 5(=1+4) bits.

Rank information is basically used to select/calculate other feedbackinformation, such that it is necessary to robustly transmit the rankinformation. Thus, it is preferable that the number of bits contained ina subframe corresponding to rank transmission be reduced as much aspossible. For such transmission, a method for reducing the number ofbits of the i1 indicator may be used as necessary. Considering theabove-mentioned condition, Table 28 exemplarily shows bit numberscapable of being used for i1 and i2 (i1/i2) for each rank.

TABLE 28 Rank (i1/i2) 1 (3/4), (3/3), (3/2), (2/4), (2/3), (2/2) 2(3/4), (3/3), (3/2), (2/4), (2/3), (2/2) 3 (2/4), (2/3), (2/2), (2/1),(2/0), (1/4), (1/3), (1/2), (1/1), (1/0) 4 (2/3), (2/2), (2/1), (2/0),(1/3), (1/2), (1/1) 5 (2/0), (1/0) 6 (2/0), (1/0) 7 (2/0), (1/0) 8 (0/0)

In case of setting the subset of the i1/i2 indicators, for example, thei1 and i2 subsets may be designed to have different sizes according to apreferred rank. In another example, the i1 and i2 subsets may bedesigned to have different sizes according to UE category. The UEcategory may be classified according to UE capability.

Embodiment 5

A method for setting the codebook subset through different precoderindexes (i1/i2) according to the present invention will hereinafter bedescribed in detail.

Table 29 shows another example of a codebook appropriate for Rank-1 CSIreporting shown in Table 11. A Rank-1 codeword may be configured on thebasis of a 4 Tx DFT vector (v_(m)), and may be represented by acombination of the 4Tx DFT vector (v_(m)) and a phase (φ_(n)). If the i1index is defined as 0 to 15 and the i2 index is defined as 0 to 15, thecodebook may be configured by both v_(m) having a 32PSK (Phase ShiftKeying) phase and φ_(n) having a QPSK (Quadrature PSK) phase. In thiscase, the same element may be repeated between contiguous indexes of thei1 value.

TABLE 29 i2 i1 0 1 2 3 4 5 6 7 0 V0 V0 V0 V0 V1 V1 V1 V1 V0 jV0 −V0 −jV0V1 jV1 −V1 −jV1 1 V2 V2 V2 V2 V3 V3 V3 V3 V2 jV2 −V2 −jV2 V3 jV3 −V3−jV3 2 V4 V4 V4 V4 V5 V5 V5 V5 V4 jV4 −V4 −jV4 V5 jV5 −V5 −jV5 3 V6 V6V6 V6 V7 V7 V7 V7 V6 jV6 −V6 −jV6 V7 jV7 −V7 −jV7 4 V8 V8 V8 V8 V9 V9 V9V9 V8 jV8 −V8 −jV8 V9 jV9 −V9 −jV9 5 V10 V10 V10 V10 V11 V11 V11 V11 V10jV10 −V10 −jV10 V11 jV11 −V11 −jV11 6 V12 V12 V12 V12 V13 V13 V13 V13V12 jV12 −V12 −jV12 V13 jV13 −V13 −jV13 7 V14 V14 V14 V14 V15 V15 V15V15 V14 jV14 −V14 −jV14 V15 jV15 −V15 −jV15 8 V16 V16 V16 V16 V17 V17V17 V17 V16 jV16 −V16 −jV16 V17 jV17 −V17 −jV17 9 V18 V18 V18 V18 V19V19 V19 V19 V18 jV18 −V18 −jV18 V19 jV19 −V19 −jV19 10 V20 V20 V20 V20V21 V21 V21 V21 V20 jV20 −V20 −jV20 V21 jV21 −V21 −jV21 11 V22 V22 V22V22 V23 V23 V23 V23 V22 jV22 −V22 −jV22 V23 jV23 −V23 −jV23 12 V24 V24V24 V24 V25 V25 V25 V25 V24 jV24 −V24 −jV24 V25 jV25 −V25 −jV25 13 V26V26 V26 V26 V27 V27 V27 V27 V26 jV26 −V26 −jV26 V27 jV27 −V27 −jV27 14V28 V28 V28 V28 V29 V29 V29 V29 V28 jV28 −V28 −jV28 V29 jV29 −V29 −jV2915 V30 V30 V30 V30 V31 V31 V31 V31 V30 jV30 −V30 −jV30 V31 jV31 −V31−jV31 i2 i1 8 9 10 11 12 13 14 15 0 V2 V2 V2 V2 V3 V3 V3 V3 V2 jV2 −V2−jV2 V3 jV3 −V3 −jV3 1 V4 V4 V4 V4 V5 V5 V5 V5 V4 jV4 −V4 −jV4 V5 jV5−V5 −jV5 2 V6 V6 V6 V6 V7 V7 V7 V7 V6 jV6 −V6 −jV6 V7 jV7 −V7 −jV7 3 V8V8 V8 V8 V9 V9 V9 V9 V8 jV8 −V8 −jV8 V9 jV9 −V9 −jV9 4 V10 V10 V10 V10V11 V11 V11 V11 V10 jV10 −V10 −jV10 V11 jV11 −V11 −jV11 5 V12 V12 V12V12 V13 V13 V13 V13 V12 jV12 −V12 −jV12 V13 jV13 −V13 −jV13 6 V14 V14V14 V14 V15 V15 V15 V15 V14 jV14 −V14 −jV14 V15 jV15 −V15 −jV15 7 V16V16 V16 V16 V17 V17 V17 V17 V16 jV16 −V16 −jV16 V17 jV17 −V17 −jV17 8V18 V18 V18 V18 V19 V19 V19 V19 V18 jV18 −V18 −jV18 V19 jV19 −V19 −jV199 V20 V20 V20 V20 V21 V21 V21 V21 V20 jV20 −V20 −jV20 V21 jV21 −V21−jV21 10 V22 V22 V22 V22 V23 V23 V23 V23 V22 jV22 −V22 −jV22 V23 jV23−V23 −jV23 11 V24 V24 V24 V24 V25 V25 V25 V25 V24 jV24 −V24 −jV24 V25jV25 −V25 −jV25 12 V26 V26 V26 V26 V27 V27 V27 V27 V26 jV26 −V26 −jV26V27 jV27 −V27 −jV27 13 V28 V28 V28 V28 V29 V29 V29 V29 V28 jV28 −V28−jV28 V29 jV29 −V29 −jV29 14 V30 V30 V30 V30 V31 V31 V31 V31 V30 jV30−V30 −jV30 V31 jV31 −V31 −jV31 15 V0 V0 V0 V0 V1 V1 V1 V1 V0 jV0 −V0−jV0 V1 jV1 −V1 −jV1

Accordingly, in order to configure the subset of a codebook, a methodfor limiting a phase of a DFT matrix constructing the vector of v_(m) orthe phase of φ_(n), and a method for constructing the i1 value usingdifferent codebook elements at different i1 indexes of codebook elementscontained in one i1 value may be considered. In this way, the codebooksubset may be constructed.

According to whether the i1 or i2 subset is used, DFT vector of v_(m)and a phase of φ_(n) may be determined. For example, it is assumed that,in order to indicate the i1 value, 3 bits may be used and 8 even indexes(0, 2, 4, 6, 8, 10, 12, 14) may be used. It is also assumed that, inorder to indicate the i1 value, 3 bits may be used and 8 indexes (0, 1,2, 3, 8, 9, 10, 11) may be used. Under these assumptions, a 4Tx DFTvector having a 16PSK phase for the v_(m) value and a QPSK for the phase(φ_(n)) may be configured.

As described above, when deciding the indication bit for the i1 valueand the indication bit for the i2 value, one phase of the 4Tx DFT vectorfor constructing the v_(m) value and the other phase for constructingthe phase (φ_(n)) according to a combination of indexes appropriate forindividual bits may be represented by the following table 30.

TABLE 30 Bit for i1 Bit for i2 (elements (elements number) number) v_(m)φ_(n) 1 2 (4n, n: 0~3) 1 (0, 1) QPSK {1, j} 2 2 (4n, n: 0~3) 1 (0, 2)QPSK BPSK 3 2 (4n, n: 0~3) 2 (0~3) QPSK QPSK 4 2 (4n, n: 0~3) 2 (2m, m:0~3) QPSK + QPSK (2pi/32) BPSK 5 2 (4n, n: 0~3) 3 (0~7) QPSK + QPSK(2pi/32) QPSK 6 2 (4n, n: 0~3) 3 (0~3, 8~11) QPSK + QPSK QPSK (2 ×2pi/32) 7 2 (4n, n: 0~3) 3 (2m, m: 0~7) QPSK + QPSK BPSK (2pi/32) + QPSK(2 × 2pi/32) + QPSK (2 × 3pi/32) 8 2 (4n, n: 0~3) 4 (0~15) QPSK + QPSKQPSK (2pi/32) + QPSK (2 × 2pi/32) + QPSK (2 × 3pi/32) 9 3 (2n, n: 0~7) 1(0, 1)  8 PSK {1, j} 10 3 (2n, n: 0~7) 1 (0, 2)  8 PSK BPSK 11 3 (2n, n:0~7) 2 (0~3)  8 PSK QPSK 12 3 (2n, n: 0~7) 2 (2m, m: 0~3)  8 PSK + 8 PSK(2pi/32) BPSK 13 3 (2n, n: 0~7) 3 (0~7)  8 PSK + 8 PSK (2pi/32) QPSK 143 (2n, n: 0~7) 3 (0~3, 8~11) 16 PSK QPSK 15 3 (2n, n: 0~7) 3 (2m, m:0~7) 32 PSK BPSK 16 3 (2n, n: 0~7) 4 (0~15) 32 PSK QPSK 17 4 (0~15) 1(0, 1) 16 PSK {1, j} 18 4 (0~15) 1 (0, 2) 16 PSK BPSK 19 4 (0~15) 2(0~3) 16 PSK QPSK 20 4 (0~15) 2 (2m, m: 0~3) 32 PSK BPSK 21 4 (0~15) 3(0~7) 32 PSK QPSK 22 4 (0~15) 3 (0~3, 8~11) 16 PSK (Overraped) QPSK 23 4(0~15) 3 (2m, m: 0~7) 32 PSK (Overraped) BPSK 24 4 (0~15) 4 (0~15) 32PSK (Overraped) QPSK

Table 31 shows another example of a codebook appropriate for Rank-2 CSIreporting shown in Table 12. In the Rank-2 CSI report, 16 indexes (0 to15) are defined for each of the i1 and i2 values.

TABLE 31 i2 0 1 2 3 1^(st) 2^(nd) 1^(st) 2^(nd) 1^(st) 2^(nd) 1^(st)2^(nd) i1 0 2 1 3 4 6 5 7 0 V0 V0 V0 V0 V1 V1 V1 V1 V0 −V0 jV0 −jV0 V1−V1 jV1 −jV1 1 V2 V2 V2 V2 V3 V3 V3 V3 V2 −V2 jV2 −jV2 V3 −V3 jV3 −jV3 2V4 V4 V4 V4 V5 V5 V5 V5 V4 −V4 jV4 −j V4 V5 −V5 jV5 −j V5 3 V6 V6 V6 V6V7 V7 V7 V7 V6 −V6 jV6 −j V6 V7 −V7 jV7 −j V7 4 V8 V8 V8 V8 V9 V9 V9 V9V8 −V8 jV8 −j V8 V9 −V9 jV9 −j V9 5 V10 V10 V10 V10 V11 V11 V11 V11 V10−V10 jV10 −j V10 V11 −V11 jV11 −j V11 6 V12 V12 V12 V12 V13 V13 V13 V13V12 −V12 jV12 −j V12 V13 −V13 jV13 −j V13 7 V14 V14 V14 V14 V15 V15 V15V15 V14 −V14 jV14 −j V14 V15 −V15 jV15 −j V15 8 V16 V16 V16 V16 V17 V17V17 V17 V16 −V16 jV16 −j V16 V17 −V17 jV17 −j V17 9 V18 V18 V18 V18 V19V19 V19 V19 V18 −V18 jV18 −j V18 V19 −V19 jV19 −j V19 10 V20 V20 V20 V20V21 V21 V21 V21 V20 −V20 jV20 −j V20 V21 −V21 jV21 −j V21 11 V22 V22 V22V22 V23 V23 V23 V23 V22 −V22 jV22 −j V22 V23 −V23 jV23 −j V23 12 V24 V24V24 V24 V25 V25 V25 V25 V24 −V24 jV24 −j V24 V25 −V25 jV25 −j V25 13 V26V26 V26 V26 V27 V27 V27 V27 V26 −V26 jV26 −j V26 V27 −V27 jV27 −j V27 14V28 V28 V28 V28 V29 V29 V29 V29 V28 −V28 jV28 −j V28 V29 −V29 jV29 −jV29 15 V30 V30 V30 V30 V31 V31 V31 V31 V30 −V30 jV30 −j V30 V31 −V31jV31 −j V31 i2 4 5 6 7 1^(st) 2^(nd) 1^(st) 2^(nd) 1^(st) 2^(nd) 1^(st)2^(nd) i1 8 10 9 11 12 14 13 15 0 V2 V2 V2 V2 V3 V3 V3 V3 V2 −V2 jV2−jV2 V3 −V3 jV3 −jV3 1 V4 V4 V4 V4 V5 V5 V5 V5 V4 −V4 jV4 −j V4 V5 −V5jV5 −j V5 2 V6 V6 V6 V6 V7 V7 V7 V7 V6 −V6 jV6 −j V6 V7 −V7 jV7 −j V7 3V8 V8 V8 V8 V9 V9 V9 V9 V8 −V8 jV8 −j V8 V9 −V9 jV9 −j V9 4 V10 V10 V10V10 V11 V11 V11 V11 V10 −V10 jV10 −j V10 V11 −V11 jV11 −j V11 5 V12 V12V12 V12 V13 V13 V13 V13 V12 −V12 jV12 −j V12 V13 −V13 jV13 −j V13 6 V14V14 V14 V14 V15 V15 V15 V15 V14 −V14 jV14 −j V14 V15 −V15 jV15 −j V15 7V16 V16 V16 V16 V17 V17 V17 V17 V16 −V16 jV16 −j V16 V17 −V17 jV17 −jV17 8 V18 V18 V18 V18 V19 V19 V19 V19 V18 −V18 jV18 −j V18 V19 −V19 jV19−j V19 9 V20 V20 V20 V20 V21 V21 V21 V21 V20 −V20 jV20 −j V20 V21 −V21jV21 −j V21 10 V22 V22 V22 V22 V23 V23 V23 V23 V22 −V22 jV22 −j V22 V23−V23 jV23 −j V23 11 V24 V24 V24 V24 V25 V25 V25 V25 V24 −V24 jV24 −j V24V25 −V25 jV25 −j V25 12 V26 V26 V26 V26 V27 V27 V27 V27 V26 −V26 jV26 −jV26 V27 −V27 jV27 −j V27 13 V28 V28 V28 V28 V29 V29 V29 V29 V28 −V28jV28 −j V28 V29 −V29 jV29 −j V29 14 V30 V30 V30 V30 V31 V31 V31 V31 V30−V30 jV30 −j V30 V31 −V31 jV31 −j V31 15 V0 V0 V0 V0 V1 V1 V1 V1 V0 −V0jV0 −jV0 V1 −V1 jV1 −jV1 i2 8 9 10 11 1^(st) 2^(nd) 1^(st) 2^(nd) 1^(st)2^(nd) 1^(st) 2^(nd) i1 0 6 1 7 4 10 5 9 0 V0 V1 V0 V1 V1 V2 V1 V2 V0−V1 jV0 −jV1 V1 −V2 jV1 −jV2 1 V2 V3 V2 V3 V3 V4 V3 V4 V2 −V3 jV2 −jV3V3 −V4 jV3 −j V4 2 V4 V5 V4 V5 V5 V6 V5 V6 V4 −V5 jV4 −j V5 V5 −V6 jV5−j V6 3 V6 V7 V6 V7 V7 V8 V7 V8 V6 −V7 jV6 −j V7 V7 −V8 jV7 −j V8 4 V8V9 V8 V9 V9 V10 V9 V10 V8 −V9 jV8 −j V9 V9 −V10 jV9 −j V10 5 V10 V11 V10V11 V11 V12 V11 V12 V10 −V11 jV10 −j V11 V11 −V12 jV11 −j V12 6 V12 V13V12 V13 V13 V14 V13 V14 V12 −V13 jV12 −j V13 V13 −V14 jV13 −j V14 7 V14V15 V14 V15 V15 V16 V15 V16 V14 −V15 jV14 −j V15 V15 −V16 jV15 −j V16 8V16 V17 V16 V17 V17 V18 V17 V18 V16 −V17 jV16 −j V17 V17 −V18 jV17 −jV18 9 V18 V19 V18 V19 V19 V20 V19 V20 V18 −V19 jV18 −j V19 V19 −V20 jV19−j V20 10 V20 V21 V20 V21 V21 V22 V21 V22 V20 −V21 jV20 −j V21 V21 −V22jV21 −j V22 11 V22 V23 V22 V23 V23 V24 V23 V24 V22 −V23 jV22 −j V23 V23−V24 jV23 −j V24 12 V24 V25 V24 V25 V25 V26 V25 V26 V24 −V25 jV24 −j V25V25 −V26 jV25 −j V26 13 V26 V27 V26 V27 V27 V28 V27 V28 V26 −V27 jV26 −jV27 V27 −V28 jV27 −j V28 14 V28 V29 V28 V29 V29 V30 V29 V30 V28 −V29jV28 −j V29 V29 −V30 jV29 −j V30 15 V30 V31 V30 V31 V31 V0 V31 V0 V30−V31 jV30 −j V31 V31 −V0 jV31 −jV0 i2 12 13 14 15 1^(st) 2^(nd) 1^(st)2^(nd) 1^(st) 2^(nd) 1^(st) 2^(nd) i1 0 14 1 13 4 14 5 15 0 V0 V3 V0 V3V1 V3 V1 V3 V0 −V3 jV0 −jV3 V1 −V3 jV1 −jV3 1 V2 V5 V2 V5 V3 V5 V3 V5 V2−V5 jV2 −j V5 V3 −V5 jV3 −j V5 2 V4 V7 V4 V7 V5 V7 V5 V7 V4 −V7 jV4 −jV7 V5 −V7 jV5 −j V7 3 V6 V9 V6 V9 V7 V9 V7 V9 V6 −V9 jV6 −j V9 V7 −V9jV7 −j V9 4 V8 V11 V8 V11 V9 V11 V9 V11 V8 −V11 jV8 −j V11 V9 −V11 jV9−j V11 5 V10 V13 V10 V13 V11 V13 V11 V13 V10 −V13 jV10 −j V13 V11 −V13jV11 −j V13 6 V12 V15 V12 V15 V13 V15 V13 V15 V12 −V15 jV12 −j V15 V13−V15 jV13 −j V15 7 V14 V17 V14 V17 V15 V17 V15 V17 V14 −V17 jV14 −j V17V15 −V17 jV15 −j V17 8 V16 V19 V16 V19 V17 V19 V17 V19 V16 −V19 jV16 −jV19 V17 −V19 jV17 −j V19 9 V18 V21 V18 V21 V19 V21 V19 V21 V18 −V21 jV18−j V21 V19 −V21 jV19 −j V21 10 V20 V23 V20 V23 V21 V23 V21 V23 V20 −V23jV20 −j V23 V21 −V23 jV21 −j V23 11 V22 V25 V22 V25 V23 V25 V23 V25 V22−V25 jV22 −j V25 V23 −V25 jV23 −j V25 12 V24 V27 V24 V27 V25 V27 V25 V27V24 −V27 jV24 −j V27 V25 −V27 jV25 −j V27 13 V26 V29 V26 V29 V27 V29 V27V29 V26 −V29 jV26 −j V29 V27 −V29 jV27 −j V29 14 V28 V31 V28 V31 V29 V31V29 V31 V28 −V31 jV28 −j V31 V29 −V31 jV29 −j V31 15 V30 V1 V30 V1 V31V1 V31 V1 V30 −V1 jV30 −jV1 V31 −V1 jV31 −jV1

When the indication bit for the i1 value and the indication bit for thei2 value are decided in the codebook subset configuration, a phase ofthe 4Tx DFT vector constructing the v_(m) value and a phase of φ_(n)according to a combination of indexes appropriate for each bit may berepresented by Table 30.

The DFT vector of v_(m) and the phase of φ_(n) are determined accordingto whether the i1 or i2 subset is used. As shown in Table 31, whendeciding the indication bit for the i1 value and the indication bit forthe i2 value, one phase of the 4Tx DFT vector for constructing the v_(m)value and the other phase for constructing the phase (φ_(n)) accordingto a combination of indexes appropriate for each bit may be representedby the following table 32.

TABLE 32 Bit for i1 Bit for i2 (elements (elements number) number) v_(m)φ_(n) 1 2 (4n, n: 0~3) 1 (0, 1) QPSK + QPSK (2pi/32) QPSK 2 2 (4n, n:0~3) 1 (0, 2) QPSK + QPSK (2pi/32) BPSK 3 2 (4n, n: 0~3) 2 (0~3) QPSK +QPSK (2pi/32) QPSK 4 2 (4n, n: 0~3) 2 (0, 1, 4, 5) QPSK + QPSK QPSK (2 ×2pi/32) 5 2 (4n, n: 0~3) 2 (2m, QPSK + QPSK (2pi/32) + BPSK m: 0~3) QPSK(2 × 2pi/32) + QPSK (2 × 3pi/32) 6 2 (4n, n: 0~3) 2 (2m + 8, QPSK + QPSK(2pi/32) + BPSK m: 0~3) QPSK (2 × 2pi/32) + QPSK (2 × 3pi/32) 7 2 (4n,n: 0~3) 3 (0~7) QPSK + QPSK (2pi/32) + QPSK QPSK (2 × 2pi/32) + QPSK (2× 3pi/32) 8 2 (4n, n: 0~3) 3 (8~15) QPSK + QPSK (2pi/32) + QPSK QPSK (2× 2pi/32) + QPSK (2 × 3pi/32) 9 2 (4n, n: 0~3) 3 (2m, QPSK + QPSK(2pi/32) + BPSK m: 0~7) QPSK (2 × 2pi/32) + QPSK (2 × 3pi/32) 10 2 (4n,n: 0~3) 4 (0~15) QPSK + QPSK (2pi/32) + QPSK QPSK (2 × 2pi/32) + QPSK (2× 3pi/32) 11 3 (2n, n: 0~7) 1 (0, 1)  8 PSK QPSK 12 3 (2n, n: 0~7) 1 (0,2) 16 PSK BPSK 13 3 (2n, n: 0~7) 1 (8, 9)  8 PSK QPSK 14 3 (2n, n: 0~7)1 (8, 10) 16 PSK BPSK 15 3 (2n, n: 0~7) 2 (0~3)  8 PSK + 8 PSK (2pi/32)QPSK 16 3 (2n, n: 0~7) 2 (0, 1, 4, 5) 16 PSK QPSK 17 3 (2n, n: 0~7) 2(2m, 32 PSK BPSK m: 0~3) 18 3 (2n, n: 0~7) 2 (2m + 8, 32 PSK BPSK m:0~3) 19 3 (2n, n: 0~7) 3 (0~7) 32 PSK QPSK 20 3 (2n, n: 0~7) 3 (8~15) 32PSK QPSK 21 3 (2n, n: 0~7) 3 (2m, 32 PSK BPSK m: 0~7) 22 3 (2n, n: 0~7)4 (0~15) 32 PSK QPSK 23 4 (0~15) 1 (0, 1) 16 PSK QPSK 24 4 (0~15) 1 (0,2) 32 PSK BPSK 25 4 (0~15) 2 (0~3) 32 PSK QPSK 26 4 (0~15) 2 (0, 1, 4,5) 16 PSK (Overraped) QPSK 27 4 (0~15) 2 (2m, 32 PSK BPSK m: 0~3) 28 4(0~15) 2 (2m + 8, 32 PSK BPSK m: 0~3) 29 4 (0~15) 3 (0~7) 32 PSK(Overraped) QPSK 30 4 (0~15) 3 (8~15) 32 PSK QPSK 31 4 (0~15) 3 (2m, 32PSK (Overraped) QPSK m: 0~7) 32 4 (0~15) 4 (0~15) 32 PSK (Overraped)QPSK 33 4 (0~15) 2 (8, 9, 10, 11) 34 4 (0~15) 2 (0, 1, 8, 9) 35 4 (0~15)2 (0, 2, 9, 10) 36 4 (0~15) 2 (8, 10, 12, 14)

Similar to the above-mentioned scheme, a method for selecting the subsetof a codebook denoted by ‘i1/i2’ may be applied to the codebooksappropriate for Rank-3 to Rank-8 of Tables 13 to 18.

For example, the i2 value of the Rank-3 codebook of Table 13 may becomposed of 16 elements (0˜15), and may be composed of a matrix thatgenerates three orthogonal beams using two vectors. Four types of Rank-3codebooks may be configured using two vectors.

For example, if i2 is composed of 0, 1, 2 and 3, four Rank-3 codebooks(Type-A, Type-B, Type-C and Type-D) may be used, and a detaileddescription thereof will hereinafter be described in detail.

In case of Type-A, a 1^(st) column is composed of W_(8i) ₁ ⁽³⁾ with apositive(+) co-phase, a 2 ^(nd) column is composed of W_(8i) ₁ ⁽³⁾ witha negative(−) co-phase, and a 3 ^(rd) column is composed of W_(8i) ₁ ₊₈⁽³⁾ with a negative(−) co-phase. [A: 1^(st) col (W_(8i) ₁ ⁽³⁾ with (+)co-phase), 2^(nd) col (W_(8i) ₁ ⁽³⁾ with (−) co-phase), and 3 ^(rd) col(W_(8i) ₁ ⁽³⁾ with (−) co-phase)].

In case of Type-B, a 1^(st) column is composed of W_(8i) ₁ ₊₈ ⁽³⁾ with apositive(+) co-phase, a 2^(nd) column is composed of W_(8i) ₁ ⁽³⁾ with anegative(−) co-phase, and a 3^(rd) column is composed of W_(8i) ₁ ⁽³⁾with a negative(−) co-phase. [B: 1^(st) col (W_(8i) ₁ ₊₈ ⁽³⁾ with (+)co-phase), 2^(nd) col (W_(8i) ₁ ⁽³⁾ with (−) co-phase), 3^(rd) col(W_(8i) ₁ ₊₈ ⁽³⁾ with (−) co-phase)].

In case of Type-C, a 1^(st) column is composed of W_(8i) ₁ ⁽³⁾ with apositive(+) co-phase, a 2^(nd) column is composed of W_(8i) ₁ ⁽³⁾ with apositive(+) co-phase, and a 3^(rd) column is composed of W_(8i) ₁ ⁽³⁾with a negative(−) co-phase. [C: 1^(st) col (W_(8i) ₁ ⁽³⁾ with (+)co-phase), 2^(nd) col (W_(8i) ₁ ⁽³⁾ with (+) co-phase), 3^(rd) col(W_(8i) ₁ ₊₈ ⁽³⁾ with (−) co-phase)].

In case of Type-D, a 1^(st) column is composed of W_(8i) ₁ ₊₈ ⁽³⁾ with apositive(+) co-phase, a 2^(nd) column is composed of W_(8i) ₁ ⁽³⁾ with apositive(+) co-phase, and a 3^(rd) column is composed of W_(8i) ₁ ⁽³⁾with a negative(−) co-phase. [D: 1^(st) col (W_(8i) ₁ ₊₈ ⁽³⁾ with (+)co-phase), 2^(nd) col (W_(8i) ₁ ⁽³⁾ with (+) co-phase), 3^(rd) col(W_(8i) ₁ ⁽³⁾ with (−) co-phase)].

In the above-mentioned examples, two vectors for use in the codebook areone vector W_(8i) ₁ ⁽³⁾ and the other vector W_(8i) ₁ ₊₈ ⁽³⁾. In case ofi2=0 and i2=2, the W_(8i) ₁ ⁽³⁾ vector is used for the first column. Incase of i2=1 and i2=3, the W_(8i) ₁ ₊₈ ⁽³⁾ vector is used for the firstcolumn. In addition, in case of i2=0 and i2=1, two different vectors(i.e., W_(8i) ₁ ⁽³⁾ and W_(8i) ₁ ₊₈ ⁽³⁾ vectors) are applied to thesecond and third columns, such that orthogonality may be achievedbetween two columns. On the other hand, in case of i2=2 and i2=3, onevector (i.e., W_(8i) ₁ ⁽³⁾ or W_(8i) ₁ ₊₈ ⁽³⁾ vector) may be applied tothe second and third columns, such that orthogonality may be obtainedusing different co-phase components (i.e., (+) and (−) co-phases).

When comparing one case of (i2=0, 1, 2, 3) at the Rank-3 codebook ofTable 13 with the case of (i2=4, 5, 6, 7) at the Rank-3 codebook ofTable 13, it can be recognized that constituent vectors of the codebookare different from each other. That is, in association with the case of(i2=0, 1, 2, 3), W_(8i) ₁ ⁽³⁾ and W_(8i) ₁ ₊₈ ⁽³⁾ vectors are used. Inassociation with the other case of (i2=4, 5, 6, 7), W_(8i) ₁ ₊₂ ⁽³⁾ andW_(8i) ₁ ₊₁₀ ⁽³⁾ vectors are used.

By means of the above-mentioned types (Type-A, Type-B, Type-C, andType-D, a Rank-3 codebook generation matrix may also be represented bythe following Table 33.

TABLE 33 I2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 I1 A B C D A B C D A BC D A B C D 0 W_(8i) ₁ ⁽³⁾, W_(8i) ₁ ₊₈ ⁽³⁾ W_(8i) ₁ ₊₂ ⁽³⁾, W_(8i) ₁₊₁₀ ⁽³⁾ W_(8i) ₁ ₊₄ ⁽³⁾, W_(8i) ₁ ₊₁₂ ⁽³⁾ W_(8i) ₁ ₊₆ ⁽³⁾, W_(8i) ₁ ₊₁₄⁽³⁾ 1 W_(8i) ₁ ₊₈ ⁽³⁾, W_(8i) ₁ ₊₁₆ ⁽³⁾ W_(8i) ₁ ₊₁₀ ⁽³⁾, W_(8i) ₁ ₊₁₈⁽³⁾ W_(8i) ₁ ₊₁₂ ⁽³⁾, W_(8i) ₁ ₊₂₀ ⁽³⁾ W_(8i) ₁ ₊₁₄ ⁽³⁾, W_(8i) ₁ ₊₂₂⁽³⁾ 2 W_(8i) ₁ ₊₁₆ ⁽³⁾, W_(8i) ₁ ₊₂₄ ⁽³⁾ W_(8i) ₁ ₊₁₈ ⁽³⁾, W_(8i) ₁ ₊₂₆⁽³⁾ W_(8i) ₁ ₊₂₀ ⁽³⁾, W_(8i) ₁ ₊₂₈ ⁽³⁾ W_(8i) ₁ ₊₂₂ ⁽³⁾, W_(8i) ₁ ₊₃₀⁽³⁾ 3 W_(8i) ₁ ₊₂₄ ⁽³⁾, W_(8i) ₁ ⁽³⁾ W_(8i) ₁ ₊₂₆ ⁽³⁾, W_(8i) ₁ ₊₂ ⁽³⁾W_(8i) ₁ ₊₂₈ ⁽³⁾, W_(8i) ₁ ₊₄ ⁽³⁾ W_(8i) ₁ ₊₃₀ ⁽³⁾, W_(8i) ₁ ₊₆ ⁽³⁾

As a method for reducing the size of bits requisite for codebookindication, the sub-sampling application may be used.

For example, 2 indication bits constructing the Rank-3 codebook may bereduced to exemplary bits shown in Table 34.

TABLE 34 I1 I2 Total bit size 2 4 6 1 4 5 2 3 5 0 4 4 1 3 4 2 2 4

In order to allow the entire bit size for codebook indication to becomposed of 4 bits, three schemes (i.e., i1+i2=0+4, 1+3, 2+2) may beused as necessary. From among the three schemes, if is composed of 0bit, namely, if ‘i1’ is composed of one element, beam resolution isdeteriorated, resulting in a reduction in performance or throughout.Next, the remaining schemes other than the scheme of using ‘i1’ composedof 0 bit will hereinafter be described in detail.

First, various methods for constructing the i1 subset and the i2 subseton the condition that one bit (1 bit) is assigned to and 3 bits areassigned to ‘i2’ will hereinafter be described.

In case of selecting/using the subset from among all indexes of i1 andi2, the element of a codebook capable of being generated according towhich index is selected is changed to another element, such that it ispreferable that indexes be properly selected to construct ahigh-performance codebook.

If i1 is composed of 1 bit, two indexes may be selected from amongseveral indexes (0, 1, 2, 3) of the i1 composed of 1 bit. The number ofvectors capable of being used as constituent elements of the codebook isset to 12 or 16 according to which index is selected from among indexes(0, 1, 2, 3) of i1. For example, provided that (0, 1) may be selectedfrom among indexes (0, 1, 2, 3) of i1, i2 vectors of W_(8i) ₁ _(+m) ⁽³⁾,(m=0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22) may be used. In anotherexample, provided that (0, 2) may be selected from among indexes (0, 1,2, 3) of i1, i6 vectors of W_(8i) ₁ _(+m) ⁽³⁾ (m=0, 2, 4, 6, 8, 10, 12,14, 16, 18, 20, 22, 24, 26, 28, 30) may be used. That is, if i1 is setto (0, 1) [i.e., i1=(0, 1)], duplicated or overlapping vectors may beapplied to each of i1=0 and i1=1. If i1 is set to (0, 2) [i.e., i1=(0,2)], different vectors may be applied to each of i1=0 and i1=2.Therefore, it is preferable that i1=(0, 2) be used from the viewpoint ofbeam resolution.

On the other hand, if i2 is assigned 3 bits, 8 indexes may be selectedfrom among 16 i2 indexes from 0 to 15. A first method for selecting 8indexes is designed to select the i2 index including various vectors soas to increase beam resolution. A second method for selecting 8 indexesperforms index selection to include all of four types (Type-A, Type-B,Type-C, Type-D) constructing a Rank-3 element.

For example, the first method selects two groups from among fouri2-index groups [(0, 1, 2, 3), (4, 5, 6, 7), (8, 9, 10, 11), (12, 13,14, 15)] such that it may use 8 indexes. For example, provided that 8indexes [(0, 2), (4, 6), (8, 10), (12, 14)] are selected as the i2index, Rank-3 codebook elements based on Type-A and Type-C may begenerated using 8 vectors. In another example, provided that 8 indexes[(1, 3), (5, 7), (9, 11), (13, 15)] are selected as the i2 indexes,Rank-3 codebook elements based on Type-B and Type-D may be generatedusing 8 vectors.

For example, the second method may select two groups from among fourgroups [(0, 1, 2, 3), (4, 5, 6, 7), (8, 9, 10, 11), (12, 13, 14, 15)]such that it may use 8 indexes. In case of the matrix constructing aRank-3 codebook, +1 and −1 may be used as co-phase components. Inaddition, there are vectors capable of forming 8 Tx DFT vectors byco-phase components. For example, provided that (+1) is used as theco-phase element in case of vectors numbered 0, 8, 16 and 24, 8 Tx DFTvectors may be formed. In another example, provided that (−1) is used asthe co-phase element in case of vectors numbered 4, 14, 20 and 28, 8 TxDFT vectors may be formed. Considering the co-polarized antennastructure, the use of 8 Tx DFT vectors may achieve high throughput orperformance.

Since the co-phase components used in the matrix constructing the Rank-3codebook are set to (+1) and (−1), it is preferable that the i2 index beselected to include Nos. 0, 8, 16, 4, 14, 20, and 28 vectors capable offorming the 8Tx DFT vector using the above-mentioned co-phasecomponents. For example, (0, 1, 2, 3) and (8, 9, 10, 11) may be selectedas the i2 indexes.

Next, in the case where 2 bits are assigned to ‘i1’ and 2 bits areassigned to ‘i2’, various methods for constructing the i2 subset willhereinafter be described in detail. Since i1 includes indexes Nos. 0, 1,2 and 3, all indexes can be represented through 2 bits.

For example, in order to select the subset of the i2 index when the i2indexes 0 to 15 are classified into four groups [(0, 1, 2, 3), (4, 5, 6,7), (8, 9, 10, 11), and (12, 13, 14, 15)], one group is selected fromamong the four groups so that four elements of the corresponding groupmay be used. One index is selected from among each of the four groupssuch that four elements may be configured. Alternatively, two groups areselected from among four groups, and two indexes are selected from amongthe selected group such that four elements may be configured.

The number of cases, each of which can selectively use two of four types(Type-A, Type-B, Type-C, and Type-D) constructing the Rank-3 codebookelement, is set to 6, respective cases are (A, B), (A, C), (A, D), (B,C), (B, D), and (C, D).

In addition, the number of cases, each of which can selectively use twoof four groups of the i2 index, is set to 6. If the frontmost vectorfrom among the i2 index groups refers to the corresponding group,respective groups may be represented by Nos. 0, 4, 8, and 12 groups.Respective cases, each of which selects two of four groups, are (0, 4),(0, 8), (0, 12), (4, 8), (4, 12), and (8, 12).

As a combination of six cases about a method for constructing the Rank-3codebook element and six cases about a method for selecting a vectorgroup, a method for constructing subsets of a total of 36 i2 indexes isachieved.

According to the above-mentioned examples, in the case where, inassociation with the Rank-3 codebook, one bit is assigned to ‘i1’ and 3bits are assigned to ‘i2’, and 2 bits are assigned to ‘i1’ and 2 bitsare assigned to ‘i2’, examples constructing the i2 and i2 subsets may berepresented by the following Table 35.

TABLE 35 i1 i2 Bit (index) Bit (index) 1 (0, 1) 3 (0, 2) (4, 6) (8, 10)(12, 14) 1 (0, 1) 3 (1, 3) (5, 7) (9, 11) (13, 15) 1 (0, 1) 3 (0, 1) (4,5) (8, 9) (12, 13) 1 (0, 1) 3 (2, 3) (6, 7) (10, 11) (14, 15) 1 (0, 1) 3(0, 1, 2, 3) (8, 9, 10, 11) 1 (0, 1) 3 (0, 1, 2, 3) (4, 5, 6, 7) 1(0, 1) 3 (4, 5, 6, 7) (12, 13, 14, 15) 1 (0, 1) 3 (0, 2) (4, 6) (8, 10)(12, 14) 1 (0, 1) 3 (1, 3) (5, 7) (9, 11) (13, 15) 1 (0, 1) 3 (0, 1) (4,5) (8, 9) (12, 13) 1 (0, 1) 3 (2, 3) (6, 7) (10, 11) (14, 15) 1 (0, 1) 3(0, 1, 2, 3) (8, 9, 10, 11) 1 (0, 1) 3 (0, 1, 2, 3) (4, 5, 6, 7) 1(0, 1) 3 (4, 5, 6, 7) (12, 13, 14, 15) 2 (0, 1, 2, 3) 2 (0, 1, 2, 3) 2(0, 1, 2, 3) 2 (4, 5, 6, 7) 2 (0, 1, 2, 3) 2 (8, 9, 10, 11) 2 (0, 1, 2,3) 2 (12, 13, 14, 15) 2 (0, 1, 2, 3) 2 (0, 4, 8, 12) 2 (0, 1, 2, 3) 2(1, 5, 9, 13) 2 (0, 1, 2, 3) 2 (2, 6, 10, 14) 2 (0, 1, 2, 3) 2 (3, 7,11, 15) 2 (0, 1, 2, 3) 2 (0, 2, 4, 6) 2 (0, 1, 2, 3) 2 (0, 2, 8, 9) 2(0, 1, 2, 3) 2 (1, 3, 5, 7) 2 (0, 1, 2, 3) 2 (1, 3, 10, 11)

Even in the case where the Rank-4 codebook is configured, the followingsubsampling may be used. For example, two indicators (i1 and i2)constructing the above-mentioned Rank-3 codebook may be reduced as shownin the following Table 36.

TABLE 36 I1 I2 Total bit size 2 3 5 1 3 4 2 2 2

In association with the Rank-4 codebook, the subsets of the i1 and i2indexes can be selected in a similar way to the scheme for selecting thesubset from among the above-mentioned Rank-3 codebook. The same partsmay herein be omitted for convenience and clarity of description.

In the Rank-4 codebook, in case that one bit is assigned to ‘i1’ and 3bits are assigned to ‘i2’, and in another case that 2 bits are assignedto ‘i1’ and 2 bits are assigned to ‘i2’, examples for constructing thei2 subset and the i2 subset can be represented by the following Table33.

TABLE 37 i1 i2 Bit (index) Bit (index) 1 (0, 1) 3 1 (0, 2) 3 2 (0, 1, 2,3) 2 (0, 1, 2, 3) 2 (0, 1, 2, 3) 2 (4, 5, 6, 7) 2 (0, 1, 2, 3) 2 (0, 1,4, 5) 2 (0, 1, 2, 3) 2 (2, 3, 6, 7) 2 (0, 1, 2, 3) 2 (0, 2, 4, 6) 2 (0,1, 2, 3) 2 (1, 3, 5, 7)

On the other hand, the selected codebook subset may be used to reportPUSCH. For example, during the mode for reporting a PMI for each subbandas shown in the PUSCH report mode 1-2, the i1 and i2 subsets may be usedto reduce PMI feedback overhead. In this case, in association with ‘i1’,one index may be reported at WB, and in association with ‘i2’, indexesfor each SB may be reported.

In addition, the 3GPP LTE Release-10 system may use a specific mode forreporting SB CQI and SB PMI as a new PUSCH report mode. Even in theabove-mentioned report mode, the codebook subset may be used to reducethe number of report bits for indicating the codebook. In this case, inassociation with ‘i1’, one index may be reported at WB, and inassociation with ‘i2’, indexes for each SB may be reported.

Embodiment 6

In Embodiment 6, a mode for periodically reporting multiple controlinformation over a PUCCH is defined, and a method for determiningtransmission priority applicable to control information reporting willhereinafter be described in detail.

As previously stated in Table 5, various control information (RI, PMI,CQI) may be periodically fed back according to PUCCH reporting modes(Modes 1-0, 1-1, 2-0, and 2-1). Periodic feedback of the UE may besemi-statically established by a higher layer. A PUCCH reporting modemay be properly applied to corresponding DL transmission according towhether DL transmission is single antenna transmission, transmissiondiversity transmission, closed-loop spatial multiplexing (SM)transmission, dual layer transmission, or the like. In addition, theCQI/PMI/RI feedback type for the PUCCH reporting mode may be classifiedinto Type 1, Type 2, Type 3 and Type 4. Type 1 is CQI feedback for theUE selected subband. Type 2 is a WB CQI feedback and a WB PMI feedback.Type 3 is RI feedback. Type 4 is WB CQI feedback.

On the other hand, the legacy 3GPP LTE Release-8 or Release-9 system hasdefined control information capable of being dropped in the case wherevarious control information collides with each other in UL transmission(i.e., in the case where control information is transmitted in the samesubframe).

In more detail, in case of feedback over a PUCCH, when RI transmissioncollides with a WB CQI/PMI (i.e., when the RI and the WB CQI/PMI aretransmitted in the same subframe), the WB CQI/PMI may be dropped.Alternatively, if RI transmission collides with an SB CQI in case ofsuch PUCCH feedback, the SB CQI may be dropped. In addition, if thepositive SR and the RI/PMI/CQI collide with each other, the RI/PMI/CQImay be dropped. In addition, if an uplink shared channel (UL-SCH) towhich the subframe bundling operation is applied collides with theperiodic RI/PMI/CQI reporting, the periodic CQI/PMI/RI reporting may bedropped in the corresponding subframe. The periodic CQI/PMI and/or RImay not be multiplexed with PUSCH transmission of the correspondingsubframe. In addition, assuming that HARQ-ACK and RI/PMI/CQI collidewith each other in a subframe in which no PUSCH is transmitted, if apredetermined parameter (simultaneousAckNackAndCQI) provided from ahigher layer is set to 1, CQI/PMI/RI is multiplexed with HARQ-ACK on aPUCCH, and otherwise the CQI/PMI/RI may be dropped.

As described above, assuming that multiple control information must besimultaneously transmitted during one subframe in 3GPP Release 8/9,limited control information must be reported. The transmission priorityapplied to control information collision may be arranged in the order ofSR, HARQ-ACK, UL-SCH (in case of the subframe bundling operation)>RI>WBCQI/PMI, WB CQI, SB CQI. In a system supporting the extended antennaconfiguration, different indexes (i1 and i2) for the precoder may be fedback. Accordingly, it is necessary to determine transmission priorityencountered in the collision between RI, I1, I2 and CQI. Prior todetermining the transmission priority of such control information, it isnecessary to define the reporting mode for defining the report timing ofthe control information.

Exemplary PUCCH Report Modes

First of all, during periodic CQI/PMI/RI transmission, CQI, CQI/PMI,preferred subband selection and CQI information may be calculated on thebasis of the last reported periodic RI, and subband selection and a CQIvalue may be calculated on the basis of the last reported periodic WBPMI and RI. In addition, two precoder indexes (I1 and I2) may bereported at different time points or at the same time point. Consideringthe above-mentioned situation, for example, the report modes shown inTable 38 may be considered for feedback information transmission.

TABLE 38 T1 T2 T3 Mode 1-1-1 (RI + I1)_WB (I2 + CQI)_WB Mode 1-1-2(RI)_WB (I1 + I2 + CQI)_WB Mode Mode 2-1(1) (RI + PTI(0)) (I1)_WB (I2 +2-1 CQI)_WB Mode 2-1(2) (RI + PTI(1)) (I2 + CQI)_WB (I2 + CQI)_SB

In Table 38, I1 and I2 may indicate indexes of the codebook composed ofprecoder elements, and PTI may indicate a precoder type indication bit.

In Mode 1-1-1 shown in Table 38, the precoder index I1 may indicate aprecoder index that is calculated/selected on the basis of RItransmitted in a current subframe. The precoder index I2 may indicate aprecoder index that is calculated/selected on the basis of the lastreported RI and the last reported IL CQI may indicate a value that iscalculated on the basis of the last reported RI, the last reported I1,and the currently reported I2.

In Mode 1-1-2 shown in Table 38, the precoder indexes I1 and I2 mayindicate precoder indexes that are calculated/selected on the basis ofthe last reported RI. CQI may indicate a value that is calculated on thebasis of the last reported RI and the currently reported I1 and I2.

In Mode 2-1(1) shown in Table 38, the precoder index I1 may indicate aprecoder index that is calculated/selected on the basis of the lastreported RI. The precoder index I2 may indicate a precoder index that iscalculated/selected on the basis of the last reported RI and the lastreported IL CQI may indicate a value that is calculated on the basis ofthe last reported RI, the last reported I1 and the current reported I2.When (11) and (I2+CQI) are reported between (RI+PTI) transmissioncycles, (11) may be reported only once and (I2+CQI) may be reportedseveral times. Alternatively, when (I1) and (I2+CQI) are reportedbetween (RI+PTI) transmission cycles, (I1) may be reported two times and(I2+CQI) may be reported several times. In another example, (I1) may besuccessively reported as necessary, or (I1) and (I2+CQI) may bealternately reported. Otherwise, (I1) may be reported just after the(RI+PTI) report time, or may be reported just before the next (RI+PTI)report time.

In Mode 2-1(2) shown in Table 38, the precoder index I2 may indicate aprecoder index that is calculated/selected on the basis of the lastreported RI. The precoder index I2 may indicate a precoder index that iscalculated/selected on the basis of the last reported RI and the lastreported IL SB CQI and SB I2 may indicate a value and indexcalculated/selected on the basis of the last reported RI and the lastreported IL

Mode 2-1 shown in Table 38 will hereinafter be described in detail.

Mode 2-1 [Mode 2-1(1) and Mode 2-1(2)] shown in Table 38 may correspondto a report mode configured in an extended form of the PUCCH report mode2-1 shown in Table 5. The PUCCH report mode 201 shown in Table 5 may bea PUCCH report mode defined in the 3GPP LTE Release-8/9 system, and isdefined as a mode for reporting WB PMI/CQI and SB CQI. In this case, SBCQI may be a CQI of an SB selected from among a BP. The term “BP” mayindicate the subset of the system bandwidth. BP defined in the systembandwidth is cyclically selected in the order of time such that a CQI ofthe BP can be reported and a plurality of SB CQIs can also be reported.In other words, RI/PMI/CQI can be reported in the same time order of(RI)→(WB PMI/CQI)→(SB CQI at first BP)→(SB CQI at second BP)→ . . . →(SBCQI at n-th BP). In this case, if the report cycle and offset of PMI/CQIare determined through RRC signaling, WB PMI/CQI and SB CQI may bereported in response to the set report cycle. RI may be established tohave a cycle corresponding to an integer multiple on the basis of thereport cycle of WB PMI/CQI. Compared to WB PMI/CQI transmission time, RImay be reported prior to a subframe corresponding to the set offsetusing the offset indicator.

For the PUCCH report mode for use in the system (e.g., 3GPP LTERelease-9 system) supporting the extended antenna structure, theextended report mode of the PUCCH report mode 2-1 shown in Table 5 maybe defined.

As the CQI/PMI/RI feedback types of the PUCCH report mode for use in the3GPP LTE Release-8/9 system, four feedback types (Type-1, Type-2,Type-3, Type-4) may be defined. Type-1 is CQI feedback for a UE-selectedsubband, Type-2 is WB CQI feedback and WB PMI feedback, Type-3 is RIfeedback, and Type-4 is WB CQI feedback. Similar to the above-mentionedfour types, four CQI/PMI/RI feedback types for use in the PUCCH reportmode of the 3GPP LTE Release-10 system may be defined. For example,Report Type 1 is RI/PTI feedback, Report Type 2 is WB I1 feedback,Report Type 3 is WB I1/CQI feedback, and Report Type 4 is SB I2/CQIfeedback. According to the Type-1 PTI setup, a report type may bedecided. For example, if Type-1 PTI is set to zero (PTI=0), Type-1,Type-2 and Type-3 may be used for such reporting. If Type-1 PTI is setto 1 (PTI=1), Type-1, Type-3 and Type-4 may be used for such reporting.Accordingly, Mode 2-1(1) and Mode 2-1(2) shown in Table 38 may bedefined.

If the precoder element is indicated using one precoder index in thesame manner as in 2Tx antenna transmission or 4Tx antenna transmission,PTI is always set to 1, such that Type-1, Type-3, and Type-4 may be usedfor the reporting. Differently from the report scheme for use in the3GPP LTE Release-8/9 system, SB PMI/CQI may be transmitted at Type-4. Inorder to enable Type-4 transmission for the 3GPP LTE Release-10 systemto operate similarly to the 3GPP LTE Release-8/9 system, one or more BPswithin the system bandwidth may be cyclically reported, and PMI/CQI fora preferred SB within BP(s) may be reported. In this case, the Type-3 orType-4 report cycle may be determined in the same manner as in thePMI/CQI cycle setup of the 3GPP LTE Release-8/9 system. For example,Type-3 and Type-4 may be reported according to a cycle set for PMI/CQI.In addition, a cycle for Type-1 can also be determined in the samemanner as in an RI cycle setup for the 3GPP LTE Release-8/9 system. Forexample, the Type-1 report cycle may be denoted by an integer multipleof the Type-3 report cycle. In addition, an offset value may beestablished in such a manner that Type-1 can be transmitted at asubframe located before a Type-3 report subframe by a predetermineddistance corresponding to a predetermined number of subframes.

On the other hand, when the precoder element is indicated using twoprecoder indexes as in 8Tx antenna transmission, (Type 1-Type 2-Type 3)or (Type 1-Type 3-Type 4) may be reported according to the PTI value.When the set of two feedback types is selected according to the PTIvalue, the report cycle for individual feedback types must be decided.Detailed methods for indicating the reporting period to be applied toeach feedback type will hereinafter be described in detail.

In a first method, if a period (or cycle) of Type 1 (RI+PTI) isestablished irrespective of PTI indication, the Type 1 (RI+PTI) periodmay be established on the basis of Type 3 (that is, Type 3 for use inthe Type 1-Type 3-Type 4 reporting mode) in case of PTI=1.

In a second method, if a period of Type 1 (RI+PTI) is establishedirrespective of PTI indication, the Type 1 (RI+PTI) period may beestablished on the basis of Type 3 (that is, Type 3 for use in the Type1-Type 2-Type 3 reporting mode) in case of PTI=0.

In a third method, if a period of Type 1 (RI+PTI) is establishedirrespective of PTI indication, the Type 1 (RI+PTI) period may beestablished on the basis of Type 2 (that is, Type 2 for use in the Type1-Type 2-Type 3 reporting mode) in case of PTI=0.

In a fourth method, a period of Type 1 (RI+PTI) may be differentlyestablished according to PTI indication. For example, in case of PTI=1,when one cycle for transmitting one Type 3 (WB I2/CQI) or at least oneType 4 (SB I2/CQI) is established, the period of Type 1 (RI+PTI (=1))may be set to an integer multiple of the above-mentioned one cycle. Onthe other hand, in case of PTI=0, when one cycle for transmitting oneType 2 (WB ID and one Type 3 (WB I2/CQI) is established, the Type 1(RI+PTI (=0)) period may be set to an integer multiple of theabove-mentioned one cycle. Minimum cycles requested for PTI=0 and PTI=1may be differently established.

In a fifth method, if one duration needed for CQI/PMI transmission atPTI=1 is different from the other duration needed for CQI/PMItransmission at PTI=0, a longer duration from among the two durationsmay be used as a reference, and feedback information is repeatedlytransmitted in the shorter duration. For example, in the case wheretransmission of one Type 2 (WB I1) and one Type 3 (WB I2/CQI) is neededfor PTI=0 and transmission of one Type 3 (WB I2/CQI) and multipletransmission of Type 4 (SB I2/CQI) are requested for PTI=1, the case ofPTI=0 may correspond to the shorter duration and the case of PTI=1 maycorrespond to the longer duration. In this case, the shorter durationmay be repeated several times such that the repeated result maycorrespond to the long duration. That is, Type 2 and/or Type 3 may berepeatedly transmitted in case of PTI=0. Upon execution of Type 2reporting, Type 3 may be repeatedly reported. Alternatively, Type 2 andType 3 may be repeatedly reported.

In a sixth method, if one duration needed for CQI/PMI transmission atPT1 is different from the other duration needed for CQI/PMI transmissionat PTI=0, a shorter duration from among the two durations may be used asa reference. In the longer duration, some report contents needed fortransmission may be dropped, or may be transmitted in the next Type 1transmission duration. For example, in the case where transmission ofone Type 2 (WB I1) and one Type 3 (WB I2/CQI) is needed for PTI=0 andtransmission of one Type 3 (WB I2/CQI) and multiple transmission of Type4 (SB I2/CQI) are requested for PTI=1, the case of PTI=0 may correspondto the shorter duration and the case of PTI=1 may correspond to thelonger duration. In this case, in the longer duration having PTI=1, someinformation (for example, Type 4) may be dropped, and one Type 3 and oneType 4 may be reported. In addition, provided that Type 4 reportsCQI/PMI using band cycling, CQI/PMI of another BP may also betransmitted according to the Type 1 transmission duration.

On the other hand, examples of the PUCCH reporting modes capable ofbeing applied to the above-mentioned 3GPP LTE Release-10 system willhereinafter be described in detail.

Since a variety of DL transmission modes are defined in the 3GPP LTERelease-10 system, a variety of PUCCH feedback reporting modes may bedefined to report a CSI for DL transmission over a PUCCH. In this case,a method for using two precoder indexes (I1 and I2) (in case of thepresent embodiment, I1 and I2 may also be referred to as PMI1 and PMI2or W1 and W2) and a method for basically using the PUCCH report modesdefined in the legacy 3GPP LTE Release 8/9 may be used. Since PUCCHtransmission resources are restricted, it is necessary to design a PUCCHreport mode in which the reporting bit width optimization using codebooksubsampling or the like is considered.

Various examples for the PUCCH feedback reporting mode applicable to the3GPP LTE Release-10 system according to the embodiments of the presentinvention will hereinafter be described in detail.

First, the size of the PUCCH report bits may not exceed 11 bits (as in3GPP LTE Release-8). Considering this situation, the bit size of eachPUCCH reporting mode must be properly established. In addition, PUCCHreport modes applied to the 3GPP LTE Release-10 system can be defined asextensions of the PUCCH reporting modes (See PUCCH reporting modes 1-1and 2-1 of Table 5) for PMI transmission in the 3GPP LTE Release-8system. Therefore, three PUCCH report modes may be defined.

PUCCH Mode-A is defined as one extension of a PUCCH Report Mode 1-1 ofTable 5, PUCCH Mode-B is defined as another extension of PUCCH ReportMode 1-1 of Table 5, and PUCCH Mode-C is defined as an extension of aPUCCH Report Mode 2-1. Mode A, Mode B and Mode C may correspond to Mode1-1-1, Mode 1-1-2, and Mode 2-1 of Table 38, respectively. In theabove-mentioned three PUCCH report modes, control informationtransmitted at one time point (i.e., at one subframe) may be expressedby a report type. Report types transmitted at individual PUCCH ReportModes A, B and C will hereinafter be described in detail.

In the PUCCH Report Mode-A, two reporting types (Type-5 and Type-2a) maybe used. Type-5 reporting is a feedback of jointly coded RI and W1, andType-2a reporting is a feedback of WB CQI and W2.

In the PUCCH Report Mode-B, two reporting types (Type-3 and Type-2b) maybe used. Type-3 is an RI feedback and Type-2b is a feedback of WB CQI,W1, and W2.

In the PUCCH Report Mode-C, four reporting types (Type-6, Type-2a,Type-7 and Type-8) may be used. Type-6 is feedback of jointly coded RIand PTI, Type-2a is a feedback of a WB CQI and W2, Type-7 is a WB W1feedback, and Type-8 is a feedback of SB CQI and W2 with an indicator ofthe selected band.

The above-mentioned reporting types are reported in different subframes,thus requiring multiple subframes (TTIs) to determine the entireprecoding matrix W and its associated CQI in the case of PUCCH Mode-Aand Mode-C.

Subsamping of PUCCH report modes will hereinafter be described indetail. PUCCH Report Mode-A and PUCCH Report Mode-B corresponding to theextended version of PUCCH Report Mode Mode 1-1 will hereinafter bedescribed.

In the case where no codebook sampling is applied to PUCCH Report Mode-Aand PUCCH Report Mode-B, feedback overhead (i.e., the number ofrequested bits) for report types may be summarized according to Rankvalues as shown in Table 39.

TABLE 39 PUCCH Mode-A Type-5 PUCCH Mode-B reporting Type-2a Type-3(Joint of RI reporting reporting Type-2b reporting Rank and W1) (W2 +CQI) (RI) (W1 + W2 + CQI) 1 6  8 (4 + 4) 3 12 (4 + 4 + 4) 2 11 (4 + [4 +3]) 15 (4 + 4 + [4 + 3]) 3 11 (4 + [4 + 3]) 13 (2 + 4 + [4 + 3]) 4 10(3 + [4 + 3]) 12 (2 + 3 + [4 + 3]) 5  7 (0 + [4 + 3])  9 (2 + 0 + [4 +3]) 6  7 (0 + [4 + 3])  9 (2 + 0 + [4 + 3]) 7  7 (0 + [4 + 3])  9 (2 +0 + [4 + 3]) 8  7 (0 + [4 + 3])  7 (0 + 0 + [4 + 3])

In Table 39, some Type-2 Reports for PUCCH Mode-B exceed 11 bits, suchthat they can also exceed the limitation of PUCCH transmission bits.Therefore, codebook subsampling may be applied to Type-2 Reporting atPUCCH Mode-B as shown in Table 40.

TABLE 40 PUCCH Mode-B Type-3 Type-2b reporting reporting Rank RI (W1 +W2 + CQI) 1 3 11 (4 + 3 + 4) W1: All, W2: 0~7 32 PSK DFT vector (nooverlapped) QPSK co-phasing 2 11 (3 + 1 + [4 + 3]) W1: 2n(n: 0~7), W2:0, 4 16 PSK DFT vector (no overlapped) BPSK co-phasing 3 11 (1 + 3 +[4 + 3]) W1: 0, 2, W2: 2m(m: 0~7) 16 PSK DFT vector (no overlapped) Twotypes of W(3) 4 11 (1 + 3 + [4 + 3]) W1: 0, 2, W2: All 16 PSK DFT vector(no overlapped) QPSK co-phasing 5  9 (2 + 0 + [4 + 3]) W1: All 16 PSKDFT vector (no overlapped) BPSK co-phasing 6  9 (2 + 0 + [4 + 3]) W1:All 16 PSK DFT vector (no overlapped) BPSK co-phasing 7  9 (2 + 0 + [4 +3]) W1: All 16 PSK DFT vector (no overlapped) BPSK co-phasing 8  7 (0 +0 + [4 + 3]) QPSK DFT vector (no overlapped) BPSK co-phasing

As can be seen from Table 39, Type-2a Reporting does not exceed 11 bitssuch that subsampling need not be used, and Type-5 Reporting may requiretwice as many bits as Type-3 Reporting. Since Type-5 and Type-3Reportings carry rank information, the Type-5 and Type-3 types shouldhave robust reliability. In the case where rank information has highpriority for PUCCH reporting and several types need to be reported inthe same subframe, CQI and PMI may drop from the RI transmissionsubframe. Considering the above-mentioned problem, codebook subsamplingmay also be applied to Type-3 Reporting so as to increase thereliability of rank feedback.

Applying subsampling to Type-5 Report may be represented, for example,by Tables 41 to 44. Tables 41 and 42 show the exemplary cases of themaximum Rank-2. Table 43 shows the exemplary case of the maximum Rank-4.Table 44 shows the exemplary case of the maximum Rank-8.

TABLE 41 PUCCH Mode-A Type-5 reporting Type-2a Joint of RI reportingRank and W1 (W2 + CQI) 1 5 (1 + 4)  8 (4 + 4) W1: All, non-overlapped 32W2: All oversampled beam QPSK co-phasing 2 11 (4 + [4 + 3])non-overlapped 32 oversampled beam QPSK co-phasing

TABLE 42 PUCCH Mode-A Type-5 reporting Type-2a reporting Rank Joint ofRI and W1 (W2 + CQI) 1 4  8 (4 + 4) W1: 2n (n: 0~7), W2: All 2 (log2(8 +8)) 11 (4 + [4 + 3])

TABLE 43 PUCCH Mode-A Type-5 reporting Type-2a Joint of RI reportingRank and W1 (W2 + CQI) 1 5 (2 + 3)  8 (4 + 4) W1: 2n non-overlapped 32(n: 0~7), oversampled beam W2: All QPSK co-phasing 2 11 (4 + [4 + 3])non-overlapped 32 oversampled beam QPSK co-phasing 3 11 (4 + [4 + 3])W1: All, non-overlapped 16 W2: All oversampled beam Two types of W(3) 410 (3 + [4 + 3]) non-overlapped 16 oversampled beam QPSK co-phasing

TABLE 44 PUCCH Mode-A Type-5 reporting Type-2a Joint of RI reportingRank and W1 (W2 + CQI) 1 5 (3 + 2)  8 (4 + 4) W1: 4n QPSK co-phasing 211 (4 + [4 + 3]) (n: 0~3), QPSK co-phasing W2: All 3 11 (4 + [4 + 3])W1: All, 16 PSK DFT vector W2: All (overlapped) Two types of W(3) 4 10(3 + [4 + 3]) 16 PSK DFT vector (no overlapped) QPSK co-phasing 5  7(0 + [4 + 3]) 16 PSK DFT vector (no overlapped) BPSK co-phasing 6  7(0 + [4 + 3]) 16 PSK DFT vector (no overlapped) BPSK co-phasing 7  7(0 + [4 + 3]) 16 PSK DFT vector (no overlapped) BPSK co-phasing 8  7(0 + [4 + 3]) QPSK DFT vector (no overlapped) BPSK co-phasing

In the example of Table 41, Type-5 bits for RI may be fixed to 5 bits,and W1 may be used as the full set, resulting in increased systemperformance or throughput.

In the example of Table 42, Type-5 bits for RI may be used as 4 bits,such that RI can be transmitted much more robustly than the example ofTable 40. On the other hand, since the subsampled W1 instead of the fullset of W1 is used, system performance or throughput of Table 42 is lowerthan that of Table 40. Meanwhile, as can be seen from Tables 42, 43 and44, W1 and W2 of Rank-1 are identical to those of Rank-2 irrespective ofthe maximum rank, resulting in the implementation of nestedcharacteristics.

Compared to the above-mentioned PUCCH Mode-A and PUCCH Mode-B, co-phaseproperties can be maintained by the codebook subsampling for the PUCCHMode-A, and at the same time beam granularity can be reduced. On theother hand, while more precise beam granularity than PUCCH Mode-A isprovided by the codebook subsampling for PUCCH Mode-B, the co-phaseproperty is unavoidably deteriorated.

PUCCH Report Mode-C corresponding to the extended version of the legacyPUCCH report mode 2-1 will hereinafter be described in detail.

Feedback overhead (the number of feedback bits) requested for PUCCHMode-C can be represented by the following Table 45.

TABLE 45 PUCCH Mode-C PUCCH Mode-C (PTI = 1) (PTI = 0) Type-2a Type-6Type-7 Type-2a Type-6 reporting Type-8 reporting reporting reportingreporting reporting (wb-W2 + wb- (sb-W2 + sb-CQI + Rank (RI + PTI) W1(wb-W2 + CQI) (RI + PTI) CQI) L-bit) 1 4 (3 + 1) 4  8 (4 + 4) 4 (3 + 1) 8 (4 + 4) 10 (4 + 4 + 2) 2 4 11 (4 + [4 + 3]) 11 (4 + [4 + 3]) 13 (4 +[4 + 3] + 2) 3 2 11 (4 + [4 + 3]) 11 (4 + [4 + 3]) 13 (4 + [4 + 3] + 2)4 2 10 (3 + [4 + 3]) 10 (3 + [4 + 3]) 12 (3 + [4 + 3] + 2) 5 2  7 (0 +[4 + 3])  7 (0 + [4 + 3])  9 (0 + [4 + 3] + 2) 6 2  7 (0 + [4 + 3])  7(0 + [4 + 3])  9 (0 + [4 + 3] + 2) 7 2  7 (0 + [4 + 3])  7 (0 + [4 + 3]) 9 (0 + [4 + 3] + 2) 8 2  7 (0 + [4 + 3])  7 (0 + [4 + 3])  9 (0 + [4 +3] + 2)

As can be seen from Table 45, if PTI is set to 1 (i.e., PTI=1) forType-6 Reporting, bits required for Type-8 Reporting at Ranks 2 to 4exceed 11 bits, such that the codebook subsampling may be applied to theexcess bits. The principle similar to that of the codebook subsamplingused for the above-mentioned PUCCH Mode-B may be applied to W2 ofType-8. In addition, as shown in Table 45, RI feedback reliability ofPUCCH Mode-C may be lower than that of the above-mentioned PUCCH Mode-Bbecause of the PTI indication of one bit. In addition, the duty cycle ofthe W1 report is longer than the duty cycle of RI. Considering thisproperty, the report time points and priorities of the reported typesmay be determined.

Priority of Feedback Information

If report modes for feedback information transmission timing are definedas described above, control information to be dropped upon collisionbetween control information in each mode will hereinafter be describedin detail.

CQI/PMI/RI information for a DL channel may be reported over a ULchannel. Transmission priority for each piece of control information maybe determined according to attributes (i.e., a reporting period, abandwidth to be applied, and a selection/calculation basis of othercontrol information) of individual control information, and as such theattributes of individual control information will hereinafter bedescribed in detail. RI bits may be determined according to a maximumnumber of layers capable of being reported. RI is generally reported ata longer term as compared to the CQI/PMI, and may be applied in units ofa system bandwidth (WB) from the viewpoint of one carrier.

PMI may be transmitted as an indicator of the codebook acting as the setof precoding matrices to be applied to DL transmission. The codebook maybe represented by a single index, or may be denoted by two differentindexes (i.e., I1 and I2). For example, in case of the codebook definedfor 2Tx or 4Tx antenna transmission in 3GPP LTE Release-8/9, theprecoder element may be determined using a single index. In case of thecodebook defined for 8Tx antenna transmission newly defined in 3GPP LTERelease-10 supporting the extended antenna configuration, the precoderelement may be determined using two different indicators (I1 and I2). Incase of using the indicators (I1 and I2), the reporting period of eachindex and the applied frequency bandwidth may be differently defined.For example, I1 may indicate a row index of the codebook. I1 may bereported at a relatively long or short term, and may be applied to asystem bandwidth (WB) defined from the standpoint of one carrier. Forexample, I2 may also indicate a column index of the codebook. I2 may bereported at relatively short term, may be applied to a system bandwidth(WB) defined from the standpoint of one carrier, and may be applied on asubband (SB) basis.

If the I1 indicator is reported at a longer term as compared to the I2indicator from the standpoint of a transmission cycle, the I1 indicatormust be reported with higher priority than the I2 indicator. In otherwords, under the condition that the I1 and I2 reports are established inthe same subframe, I1 may be transmitted and I2 may be dropped.

CQI may be calculated on the basis of the determined precoder, and maybe reported along with the I2 indicator.

Transmission priorities of feedback information will hereinafter bedescribed with reference to PUCCH report modes of Table 38.

In Mode 1-1-1 of Table 38, RI and I1 applied to a WB may be reported ata long term, and I2 and CQI applied to a WB may be reported at a shortterm. Accordingly, as can be seen from Mode 1-1-1 of Table 38, if the(R1+I1) transmission time point collides with the (I2+CQI) transmissiontime point, (I2+CQI) may be dropped. That is, the long-term reported RIand I1 may be reported at a higher priority as compared to theshort-term reported I2 and CQI.

In Mode 1-1-2 of Table 38, RI applied to WB may be reported at a longterm, and I1, I2 and CQI applied to WB may be reported at a short term.In Mode 1-1-2 of Table 38, if the RI reporting period collides with the(I1+I2+CQI) reporting period, the (I1+I2+CQI) may be dropped. That is,the long-term reported RI may be given higher priority than theshort-term reported I1, I2 and CQI.

In Mode 2-1 of Table 38, RI may have higher priority than PMI/CQI. Thatis, in Mode 2-1(1) of Table 38, if the (RI+PTI) reporting periodcollides with the (I1) or (I2+CQI) reporting period, (I1) or (I2+CQI)may be dropped. In addition, in Mode 2-1(2) of Table 38, if (RI+PTI)collides with (I2+CQI)_WB or (I2+CQI)_SB, (I2+CQI)_WB or (I2+CQI)_SB maybe dropped.

In addition, in Mode 2-1 of Table 38, attributes of the subsequentlyreported information may be determined according to PTI indication. IfPTI=0 (i.e., Mode 2-1(1)) is indicated, I1 applied to a WB, and I2 andCQI applied to a WB may be reported. In this case, I1 may be reported ata longer term than I2 and CQI, or may be reported at the same term asthe I2 and CQI. If PTI indicates the value of 1 (i.e., Mode 2-1(2)), I2and CQI applied to a WB are reported and I2 and CQI applied to a subband(SB) are reported. In this case, I2 and CQI applied to WB are reportedat a longer term as compared to I2 and CQI applied to SB. In Mode 2-1,PTI is reported along with RI and is reported at a long term.

In Mode 2-1, as to (RI, PTI), (I1)_WB, (I2, CQI)_WB and (I1, CQI)_SBtransmission cycles, the (I1)_WB may be reported at a longer term thanthe (RI, PTI). Therefore, in Mode 2-1, (I1)_WB may be reported at alonger term than the (RI, PTI)_WB. That is, if (I1)_WB collides with(RI, PTI)_WB, (RI, PTI)_WB may be dropped.

Embodiment 7

Embodiment 7 relates to a method for determining a transmission prioritycapable of being applied to multiple control information reporting onthe condition that multi-carrier or carrier aggregation is applied.

In case of multi-carrier transmission, when control information ofmultiple carriers configured in a downlink is reported from a UE to theeNB through an uplink carrier, control information can be reportedthrough one carrier (for example, UL P-cell) configured for a specificpurpose. In this case, a transmission cycle of control information foreach DL carrier may be independently configured for each carrier. Thatis, positive SR, HARQ-ACK, and CQI/PMI/RI, and the like may haveindependent transmission cycles for individual carriers and may bereported through an uplink carrier. Provided that control information istransmitted through one UL carrier, different types of controlinformation may collide with each other, such that it is necessary todetermine which control information is assigned transmission priority. Avariety of control information transmission schemes for effectivelysupporting DL multi-carrier transmission will hereinafter be describedin detail.

In a first method, if one time point at which HARQ-ACK information for apositive SR or DL multi-carriers is reported is identical to the othertime point at which CQI/PMI/RI is reported, CQI/PMI/RI may be dropped.

In a second method, CQI/PMI/RI information for each DL carrier may bereported at an independent transmission cycle, and the CQI/PMI/RIreporting priority may be determined according to DL carrier priority.For example, provided that Carrier-A has higher priority than Carrier-B,if CQI/PMI/RI of Carrier-A collides with CQI/PMI/RI of Carrier-B, theCQI/PMI/RI for Carrier-B may be dropped.

In a third method, in multi-carrier transmission, information as towhich information is to be dropped when CQI, PMI and RI collide with oneanother at the CQI/PMI/RI reporting cycle for multiple DL carriers maybe determined. Irrespective of DL carrier types, priority may beassigned according to feedback information attributes. CQI/PMI may becalculated and selected on the basis of the last reported RI. Ifmultiple indexes (for example, I1 and I1) are reported for the precoder,each precoder may be calculated and selected on the basis of the lastreported RI, and a CQI transmitted along with I1 may be calculated onthe basis of the last reported RI, the last reported I1, and thecurrently transmitted I1. Alternatively, a CQI reported along with I1/I1may be calculated on the basis of the last reported RI and the currentlyreported I1/I2. Considering the above-mentioned situation, higherpriority may be assigned to control information reported at a longerterm. For example, I1 has the highest priority, RI has priority lessthan that of I1, and I2 and CQI may have priority less than that of theRI. If low priority control information is transmitted at the same timepoint as that of the high priority control information, the low prioritycontrol information may be dropped and the high priority controlinformation may be dropped.

Embodiment 8

Embodiment 8 relates to a method for reporting the case in which certaincontrol information is dropped on the condition that multiple controlinformation is reported, and relates to a detailed reporting method foruse in the case in which RI or I1 (PMI or W1) is dropped.

On the assumption that CQI/PMI/RI is periodically reported over a PUCCHaccording to Mode 2-1 (i.e., Mode 2-1(1) and Mode 2-1(2)), the reportingmethod for use in the case in which control information is dropped willhereinafter be described in detail.

In FIG. 27, a method for transmitting control information in case ofMode 2-1 will hereinafter be described with reference to Table 46. FIG.27 illustrates examples of RI/PMI/CQI report time points in case of Mode2-1. Table 46 illustrates RI/PMI/CQI report time points and attributesin case of Mode 2-1.

TABLE 46 Case Feedback information Case 1 RI(=N) + PTI(=0) I1 (forrank-N)_WB I2, CQI (based on I1 for I2, CQI_WB rank-N)_WB RI(=M) +PTI(=0) I1 (for rank-M)_WB I2, CQI (based on I1 for I2, CQI_WBrank-M)_WB Case RI(=N) + PTI(=0) I1 (for rank-N)_WB I2, CQI (based on I1for I2, CQI_WB 2-1 rank-N)_WB

I2, CQI (based on I1 for I2, CQI_WB

Case RI(=N) + PTI(=0) I1 (for rank-N)_WB I2, CQI (based on I1 for I2,CQI_WB 2-2 rank-N)_WB RI(=N) + PTI(=1) I2, CQI (based on I1 for I2,CQI_SB I2, CQI_SB rank-N)_WB

I2, CQI (based on I1 for I2, CQI_WB

RI(=N) + PTI(=1) I2, CQI (based on I1 for I2, CQI_SB I2, CQI_SBrank-N)_WB Case RI(=N) + PTI(=0) I1 (for rank-N)_WB I2, CQI (based on I1for I2, CQI_WB 3-1 rank-N)_WB RI(=M) + PTI(=0)

I2, CQI (based on I1 for I2, CQI_WB rank-M)_WB Case RI(=N) + PTI(=0) I1(for rank-N)_WB I2, CQI (based on I1 for I2, CQI_WB 3-2 rank-N)_WBRI(=N) + PTI(=1) I2, CQI (based on I1 for I2, CQI_SB I2, CQI_SBrank-N)_WB RI(=M) + PTI(=0)

I2, CQI (based on I1 for I2, CQI_WB rank-M)_WB RI(=M) + PTI(=1) I2, CQI(based on I1 for I2, CQI_SB I2, CQI_SB rank-M)_WB

I1, I2 and CQI may be determined according to indication of the reportedRI. Referring to Case 1 of Table 46, if Rank-N information is reported,I1 is selected from among the codebook for Rank-N and then reported.Thereafter, I2 is selected on the basis of the selected I1, and CQI iscalculated and reported on the basis of the selected I1. After that, ifa rank value is changed so that the RI value is reported as Rank-M, I1and I2 are selected on the basis of Rank-M and CQI is then calculated.

On the other hand, Case 2-1 and Case 2-2 shown in Table 46 illustratecontrol feedback information attributes on the condition that RI isdropped.

Case 2-1 and Case 202 of Table 46 illustrate RI information referred byI1, I2 and CQI when RI is dropped. Provided that I1, I2 and CQI areselected and calculated on the basis of the latest reported RI, there isno problem in selecting/calculating I1, I2 and CQI although RI isdropped. In other words, in Case 2-1, if an RI indicating Rank-M isdropped, the UE may select/calculate I1, I2 and CQI on the basis of thelast reported RI rank value (i.e., N). In addition, although PTI is setto 0 or 1 as in Case 2-2, I1, I2 and CQI may be selected and calculatedaccording to the last reported rank value. In this case, it ispreferable that RI in case of PTI=1 may report the same rank informationas in RI reported rank information in case of PTI=0.

On the other hand, it should be noted that I1 may be unexpectedlydropped. I1 information may be used as information for I1 selection andCQI calculation. If I1 is dropped as soon as rank information is changedto another, there may occur some difficulty in I2 selection and CQIcalculation. For example, under the condition that rank information ischanged from N rank to M rank as shown in Case 3-1 and Case 3-2 of Table46, Rank-M based I1 is not contained in I2 and CQI to beselected/calculated later, resulting in the occurrence of an unexpectedproblem in selection/calculation. Therefore, special handling is neededto perform I1 selection and CQI calculation in the case in which I1 isdropped.

Examples of the present invention for selecting/calculating I2 and CQIwhen I2 is dropped will hereinafter be described in detail.

Embodiment 8-A

Provided that I2/CQI calculation must be carried out on the basis ofRank M, I2 and CQI can be calculated on the basis of the latest reportedI1 (for Rank-M) from among I1 values of the pre-reported Rank-M.Accordingly, I2 and CQI for Rank-M may be selected and calculatedalthough there is no I1 for the pre-reported Rank-M, as represented bythe following Table 47.

TABLE 47 Case A RI(=N) + PTI(=0) I1 (for rank-N)_WB I2, CQI (based on I1for I2, CQI_WB rank-N)_WB RI(=N) + PTI(=1) I2, CQI (based on I1 I2,CQI_SB I2, CQI_SB for rank-N)_WB RI(=M) + PTI(=0)

I2, CQI (based on I1 for I2, CQI_WB rank-M)_WB RI(=M) + PTI(=1) I2, CQI(based on I1 I2, CQI_SB I2, CQI_SB for rank-M)_WB

Embodiment 8-B

Provided that a rank is changed from a Rank N to a Rank M, if I1 forRank-M is dropped, rank information of the latest reported I1 may beoverridden.

For example, in the case where an RI for indicating a Rank-M istransmitted, I1 reporting for the Rank-M is dropped, and I2/CQI based onthe Rank-M must be selected and calculated, the latest reported I1 maybe an indicator selected on the basis of the Rank-N. In this case, thelatest reported RI and associated rank information (i.e., Rank-M) isdisregarded and I1 and CQI can be calculated on the basis of the latestreported I1 and a rank value (Rank-N) thereof. In addition, even when WBI2, CQI and SB I2/CQI must be reported according to PTI indicationreported in the next RI (indicating Rank-M) transmission cycle, theselected I1 based on a Rank-M is dropped, such that I2 and CQI can becalculated on the basis of the latest reported I1 and a rank of the I1,as represented by the following Table 48.

TABLE 48 Case B RI(=N) + PTI(=0) I1 (for rank-N)_WB I2, CQI (based on I1for I2, CQI_WB rank-N)_WB RI(=N) + PTI(=1) I2, CQI (based on I1 I2,CQI_SB I2, CQI_SB for rank-N)_WB RI(=M) + PTI(=0)

I2, CQI (based on I1 for I2, CQI_WB rank-N)_WB RI(=N) + PTI(=1) I2, CQI(based on I1 I2, CQI_SB I2, CQI_SB for rank-N)_WB

Embodiment 8-C

Provided that I1 is dropped, PTI=0 is indicated at the next RI reportingcycle such that I1 can be reported, and associated description thereofis shown in the following Table 49.

TABLE 49 Case C RI(=N) + PTI(=0) I1 (for rank-N)_WB I2, CQI (based on I1for I2, CQI_WB rank-N)_WB RI(=N) + PTI(=1) I2, CQI (based on I1 I2,CQI_SB I2, CQI_SB for rank-N)_WB RI(=N) + PTI(=1) I2, CQI (based on I1I2, CQI_SB I2, CQI_SB for rank-N)_WB RI(=M) + PTI(=0)

I2, CQI (based on I1 for I2, CQI_WB rank-M)_WB RI(=M) + PTI(=0) I1(forrank-M)_WB I2, CQI (based on I1 for I2, CQI_WB rank-M)_WB RI(=M) +PTI(=1) I2, CQI (based on I1 I2, CQI_SB I2, CQI_SB for rank-M)_WB

Embodiment 8-D

If I1 is dropped, I1 reporting is delayed, and the resultant I1 can bereported. For example, I1 may be reported at the N-th subframesubsequent to the I1 reporting time.

For example, the value of N may be established in such a manner that theN-th subframe is set to any one of CQI reporting time points after theoriginal I1 reporting time. At an arbitrary time point from among apromised cycle for CQI reporting, the dropped I1 may be reported insteadof control information that must be originally transmitted. For example,as shown in FIG. 28( a), provided that I2/CQI is scheduled to bereported upon execution of the I1 reporting, I1 may be reported insteadof reporting I2/CQI. Alternatively, at an initial CQI report time afterexecution of I1 dropping, the dropped I1 may be reported. As shown inFIG. 28( b), an N value may be established in such a manner that thedropped I1 can also be reported at an initial subframe after theoriginal I1 reporting time, as represented by the following Table 50.

TABLE 50 Case D RI(=N) + PTI(=0) I1 (for rank-N)_WB I2, CQI(based on I1I2, CQI_WB for rank-N)_WB RI(=N) + PTI(=1) I2, CQI (based on I1 I2,CQI_SB I2, CQI_SB for rank-N)_WB RI(=M) + PTI(=0)

I1 (for rank-M) I2, CQI(based on I1 for rank- M)_WB RI(=M) + PTI(=1) I2,CQI (based on I1 I2, CQI_SB I2, CQI_SB for rank-M)_WB

Embodiment 9

Embodiment 9 illustrates priority of control information transmissionwhen multiple control information is reported, and also illustrates adetailed method for establishing control information transmissionpriority for use in multi-carrier transmission.

When the 3GPP LTE system measures a DL channel and reports it over a ULchannel, RI, PMI, CQI, etc. may be reported as DL channel information.In this case, when DL channel information is reported over a PUCCH, amethod for reporting channel information over a PUCCH can be largelyclassified into two modes according to frequency granularity based onCQI/PMI. A mode for reporting CQI/PMI applied to a WB may be referred toas PUCCH reporting mode 1-1, and a mode for reporting WB CQI/PMI and SBCQI may be referred to as a PUCCH reporting mode 2-1. PUCCH has limitedchannel capacity capable of being transmitted at a time, such that arank, WB CQI/PMI, and SB CQI may be reported at different time points.FIG. 29 shows exemplary time points for reporting individual channelinformation pieces. In comparison between reporting cycles of individualchannel information pieces, RI is reported at a relatively long term,and SB CQI/PMI and SB CQI may be reported at a relatively short term.

Considering multi-carrier (carrier aggregation) transmission, each DLcarrier information must be measured and reported. DL channelinformation may be reported over one UL carrier (e.g., UL P-cell), andtime points at which each DL carrier information is reported may beestablished to have an independent transmission cycle for each DLcarrier. In this case, there may arise one case in which DL carrierinformation to be reported over one DL carrier must be reported at thesame time (that is, information pieces of different DL carriers may bereported at the same time). In order to solve the above-mentionedproblem, priority for each CSI (RI, PMI, CQI) is determined so that highpriority information may be transmitted and low priority information maybe dropped. As shown in FIG. 29, rank information may be reported at arelatively long term, CQI/PMI information may be reported at relativelyshort-term, such that transmission priority is assigned to relativelylong-term reporting information and therefore the latest channelinformation may be reported.

In order to indicate precoding information for 8Tx antenna transmissionin the 3GPP LTE-A system, a codebook for using two indexes (I1 and I2(or PMI1(W1) and PMI2(W2)) is defined. Two indexes must be reported sothat precoder element information becomes definite. I1 may be reportedas WB information at a relatively long term, and I2 may be reported asSB information at a relatively short term. Compared to CSI reporting foruse in the legacy 3GPP LTE Release 8/9 system, information as to whichscheme is used to report two codebook indicators needs to beadditionally defined. In order to report RI, I1, I2 and CQI, thefollowing PUCCH report modes such as Mode 2-1(1) and Mode 2-1(2) ofTable 38 can be applied.

As can be seen from Mode 2-1 of Table 38, attributes of the nextreported information are determined according to a precoder typeindicator (PTI). That is, if PTI transmitted along with RI is set tozero, W1 is transmitted, and WB W2 and CQI are then transmission. Inthis case, W2 and CQI are selected and calculated on the basis of thepreviously reported WL. If PTI is set to 1, WB W2/CQI is transmitted,and SB W2/CQI is then transmitted. FIG. 30 shows CSI report time pointsat PTI=0 and PTI=1 in Mode 2-1.

Considering the CSI reporting cycle, W1 is relatively slowly (lessfrequently) reported as shown in FIG. 30, and (RI+PTI) is relativelyfrequently reported as compared to W1. In addition, WB W2/CQI and SBW2/CQI are frequently reported. Therefore, as described above, whenselecting CSI to be transmitted at a specific time in multi-carriertransmission, transmission priority of each CSI may be defined asW1>RI+PTI>W2=CQI.

On the other hand, PUCCH report modes such as Mode 1-1- and Mode 1-1-2of Table 38 may also be used. Transmission priority of CSI informationmay be determined according to reporting cycles of such PUCCH reportmodes. That is, in Mode 1-1-1 of Table 38, priority of(RI+I1)_WB>(I2+CQI)_WB may be defined. In Mode 1-1-2 of Table 38,priority of (RI)_WB>(I1+I2+CQI)_WB may be defined.

In this case, (RI+I1)_WB transmission of the first DL carrier and(RI)_WB transmission of the second carrier may collide with each otherupon multi-carrier transmission.

Because I1 may be reported at a relatively longer term than RI,influence of I1 dropping may be larger than influence of RI dropping,such that I1 may have higher priority than R1. That is, priority of(RI+I1)>(RI) may be achieved.

Considering three feedback modes (Mode 1-1-1, Mode 1-1-2, and Mode 2-1)of Table 38, (I1)_WB may have the highest priority.

Embodiment 10

Embodiment 10 illustrates priority of control information transmissionwhen multiple control information is reported, and Embodiments 10-A and10-B illustrate feedback methods to be used when RI and PTI are dropped.

Embodiment 10-A

In case of a PUCCH report mode such as Mode 2-1 of Table 38, (RI+PTI)may be dropped due to various reasons. In this case, information to bereported at the next time may be determined according to the latestreported (RI+PTI) indication.

For example, if RI+PTI (=0) is reported, (W1)_WB is reported and(W2+CQI)_WB is then reported. In this case, if RI+PTI (=0) is dropped,information to be subsequently reported may be determined according tothe last reported PTI value. As can be seen from FIG. 31, if RI+PTI (=0)is dropped, the last reported PTI is set to 1 such that (W2+CQI)_WB isreported and (W2+CQI)_SB is then reported.

Embodiment 10-B

In case of a PUCCH report mode such as Mode 2-1 of Table 38, if (RI+PTI)is dropped, information to be subsequently reported may be calculatedand selected according to a rank value indicated by the latest reportedRI.

For example, if RI(=M)+PTI is reported, W1, W2, and CQI to betransmitted subsequent to the RI(=M)+PTI must be selected/calculated onthe basis of Rank-M and then reported. In this case, if RI(=M)+PTI isdropped, information to be subsequently reported may be selected andcalculated on the basis of the last reported RI rank value. In FIG. 32,if RI(=M)+PTI is dropped, W1_WB is selected and reported on the basis ofRank-N according to the last reported RI(=N) instead of Rank-M. In thiscase, the subsequent W1/CQI may be selected and calculated on the basisof Rank-N and W1 based on the Rank-N. If PTI indication time isdetermined, PTI indication may be reported according to the determinedtime.

Embodiment 11

Embodiment 11 shows the codebook subsampling method that is capable ofbeing applied to PUCCH report modes and MU-MIMO case and definition ofPUSCH reporting modes.

Embodiment 11-A

As the extended version of the legacy PUCCH report mode of the system(e.g., 3GPP LTE Release-10 system) supporting the extended antennastructure, three PUCCH report modes [(Mode 1-1-1, Mode 1-1-2, Mode 2-1)or (Mode-A, Mode-B, Mode-C)] shown in Table 39 may be applied.

Mode 1-1-1 reports the joint coded RI and I1, and reports the widebandCQI and the wideband I2. Mode 1-1-2 is a mode for transmitting (RI)_WBand (I1+I2+CQI)_WB. Mode 2-1 may transmit different feedbackinformation. If PTI is set to zero (PTI=0), (RI+PTI(0)), (I1)_WB, and(I2+CQI)_WB may be transmitted. If PTI is set to 1 (PTI=1), (RI+PTI(1)),(I2+CQI)_WB, and (I2+CQI)_SB can be transmitted. On the other hand, inthe present embodiments, two precoder indexes I1 and I2 may also berepresented by W1 and W2, respectively.

A method for implementing report bandwidth optimization by applyingcodebook subsampling to each PUCCH report mode and at the same timemaintaining PUCCH feedback coverage as in the legacy 3GPP LTERelease-8/9 will hereinafter be described in detail.

Signaling overhead requested for PUCCH Report Modes 1-1-1 and 1-1-2 areshown in Table 39. In Table 39, Mode-A corresponds to PUCCH Report Mode1-1-1, and Mode-B corresponds to PUCCH Report Mode 1-1-2.

As can be seen from Table 39, 6 bits are needed for Type-5 (joint codedRI and WI) at PUCCH Report Mode 1-1-1. Since 6 bits are assigned to RIand WI because of the joint-coded RI and WI, coverage for RItransmission is greatly lower than that of the legacy 3GPP LTE Release-8system. As a result, RI detection failure or performance deteriorationmay be encountered. Therefore, WI subsampling may be used to increase RIcoverage. In Mode 1-1-1, Type-2a (W2 and CQI) Reporting may be morefrequently updated than Type-5 Reporting, such that it can be recognizedthat Type-2a need not always be protected. Therefore, in so far as thereported bandwidth does not exceed one bit, W2 sampling need not beused.

In PUCCH Report Mode 1-1-2, RI is not joint-coded with other CSIinformation, such that RI coverage can be maintained in the same manneras in the legacy 3GPP LTE Release-8 system. However, as shown in Table39, in case of Rank-1, Rank-2, Rank-3, and Rank-4, signaling overheadexceeding 11 bits is required for Type-2b (W1+W2+CQI) Reporting.Therefore, in order to reuse PUCCH format 2 of the 3GPP LTE Release-8system, codebook sampling is needed.

First, a subsampling method capable of being applied to PUCCH ReportMode 1-1-1 will hereinafter be described in detail.

W1 candidates may be different in number according to transmissionranks. That is, as shown in Tables 11 to 18, the number of W1 candidatesmay be set to 16, 16, 4, 4, 4, 4, 4, and 1 for Ranks 1 to 8,respectively. If RI and W1 are joint-coded and reported, the requestedsignaling overhead is denoted by 6 bits (=ceiling(log 2(53))). In orderto extend the RI coverage, signaling overhead may be reduced to 4 or 5bits through W1 subsampling. Examples of the W1 subsampling are shown inthe following Table 51.

TABLE 51 Alternative W1 Alt-1 Rank-1 and 2 8 elements for each rank: (0,2, 4, 6, 8, 10, 12, 14) Rank-3 and 4 4 elements for each rank: (0, 1, 2,3) Rank-5, 6 and 7 2 elements for each rank: (0, 1) Rank-8 1 element:(0) Total number of 31 elements (5 bit) element Alt-2 Rank-1 and 2 4elements for each rank: (0, 4, 8, 12) Rank-3 and 4 2 elements for eachrank: (0, 2) Rank-5, 6, 7 and 8 1 elements for each rank: (0) Totalnumber of 16 elements (4 bit) element

In the dual-stage codebook structure, overlapped beams are presentbetween beam groups. As can be seen from the Alt-1 scheme of Table 51,although subsampling is applied to W1 by excluding only the odd W1values from the codebook, all the beams of the codebook can bemaintained. However, W1 and W2 for constructing the entire codebook aretransmitted from other subframes, such that performance deteriorationmay occur as compared to the use of the entire codebook to which nosubsampling is applied. Meanwhile, as can be seen from the Alt-2 schemeof Table 51, if subsampling capable of excluding many more beams fromthe codebook is applied, it is impossible to use some beams of thecodebook differently from the Alt-1 scheme in which all beams of thecodebook can be maintained, resulting in the occurrence of performancedeterioration.

Table 52 shows, in 8×2 SU-MIMO transmission, the system levelperformance of PUCCH Report Mode 1-1-1 based on the codebook subsamplingapplication. Table 52 shows that, under the condition that (4+4) is usedas W1 and W2 bits for Rank-1 and Rank-2 and the Alt-1 and Alt-2 schemesare applied thereto, an average spectral efficiency (SE) and a cell-edgeSE for a cross-polarized antenna structure and a co-polarized antennastructure. While the Alt-1 scheme of Table 52 generates marginalperformance deterioration in all of the average SE and the cell-edge SE,the Alt-2 scheme generates relatively high performance deterioration inthe cell-edge SE.

TABLE 52 Cross-polarized Co-polarized (0.5 λ) (4 λ) Antenna AntennaFeedback information Average Cell Average Cell (W1 + W2 for rank-1, SEEdge SE SE Edge SE W1 + W2 for rank-2) (bps/Hz) (bps/Hz) (bps/Hz)(bps/Hz) Reference (4 + 4, 4 + 4) 1.63 0.0436 1.72 0.0730   (0.00%)(0.00%)   (0.00%) (0.00%) Alt-1 (3 + 4, 3 + 4) 1.59 0.0436 1.71 0.0730(−2.00%) (0.00%) (−1.00%) (0.00%) Alt-2 (2 + 4, 2 + 4) 1.59 0.0404 1.680.0714 (−2.00%) (−7.00%)   (−2.00%) (−2.00%)  

As can be seen from Table 52, while the subsampled codebook of 5 bitsmaintains system performance, the other subsampled codebook of 4 bitsreduces system performance by a predetermined amount corresponding to amaximum of 7%. Therefore, although RI coverage of the Alt-1 scheme isrelatively lower than that of the Alt-2 scheme, the Alt-1 scheme is morepreferable than the Alt-2 scheme from the viewpoint of systemperformance.

Hereinafter, a subsampling method capable of being applied to PUCCHReport Mode 1-1-2 will be described in detail.

In the (W1+W2+CQI) report of PUCCH Report Mode 1-1-2, W1 and W2 arereported in the same subframe. Therefore, subsampling may be used tomaintain the report bandwidth of 11 bits or less. As described above, incase of the subsampling for reducing the W1 value by 1 bit (for example,in the case where 8 index subsets are selected from among 16 indexes),all the beams of the codebook can be maintained, such that systemperformance deterioration can be minimized. However, if the W1 value issubsampled by bits of more than 1 bit, a specific-directional beam groupis excluded from the codebook, such that system performance may begreatly deteriorated. Therefore, it may be preferable that, inassociation with Rank-2 to Rank-4, 1-bit subsampling is performed at W1and more bits are excluded at W2.

The following Table 53 shows exemplary subsampling methods capable ofbeing applied to PUCCH Report Mode 1-1-2.

TABLE 53 Alt W1 W2 Alt-1 Rank1 3 bit: 4 bit: (0, 1, 2, 3, 4, 5, 6, 7,(0, 2, 4, 6, 8, 10, 12, 14) 8, 9, 10, 11, 12, 13, 14, 15) Rank2 3 bit:(0, 2, 4, 6, 8, 1 bit: 10, 12, 14) (0, 1) Rank3 1 bit: 3 bit: (0, 2) (0,2, 4, 6, 8, 10, 12, 14) Rank4 1 bit: 3 bit: (0, 2) (0, 1, 2, 3, 4, 5, 6,7) Rank5~7 2 bit 0 bit Rank8 0 bit 0 bit Alt-2 Rank1 3 bit: 2 bit: (0,2, 4, 6, 8, 10, 12, 14) (0, 1, 2, 3) Rank2 3 bit: 1 bit: (0, 2, 4, 6, 8,10, 12, 14) (0, 1) Rank3 1 bit: 3 bit: (0, 2) (0, 2, 4, 6, 8, 10, 12,14) Rank4 1 bit: 3 bit: (0, 2) (0, 1, 2, 3, 4, 5, 6, 7) Rank5~7 2 bit 0bit Rank8 0 bit 0 bit

Referring to Table 53, according to the Alt-1 scheme and the Alt-2scheme, only one bit is reduced at W1 for Rank-1 to Rank-4 so as toprevent all the beam groups from being lost. Therefore, W2 is subsampledaccording to the requested bandwidth.

Table 54 shows, in 8×2 SU-MIMO transmission, the level of systemperformance of PUCCH Report Mode 1-1-1 based on the codebook subsamplingapplication. Table 54 shows, under the condition that (4+4) is used asW1 and W2 bits for Rank-1 and Rank-2 and the Alt-1 and Alt-2 schemes areapplied thereto, an average spectral efficiency (SE) and a cell-edge SEfor a cross-polarized antenna structure and a co-polarized antennastructure.

TABLE 54 Cross-polarized Co-polarized (0.5 λ) (4 λ) Antenna AntennaFeedback information Average Cell Average Cell (W1 + W2 for rank-1, SEEdge SE SE Edge SE W1 + W2 for rank-2) (bps/Hz) (bps/Hz) (bps/Hz)(bps/Hz) Reference (4 + 4, 4 + 4) 1.63 0.0416 1.72 0.0736   (0.00%)(0.00%)   (0.00%)   (0.00%) Alt-1 (3 + 4, 3 + 1) 1.60 0.0416 1.68 0.0708(−2.00%) (0.00%) (−2.00%) (−4.00%) Alt-2 (3 + 2, 3 + 1) 1.58 0.0416 1.660.0698 (−3.00%) (0.00%) (−3.00%) (−5.00%)

As can be seen from Table 54, some steering vectors of 8 Tx antennas areexcluded from W2 subsampling, such that performance deterioration of theco-polarized antenna structure is relatively larger than that of thecross-polarized antenna structure. On the other hand, there arisesmarginal performance deterioration in the cross-polarized antennastructure.

Therefore, it can be recognized that performance deterioration caused bythe use of a subsampled codebook under the condition that W1 subsampledby 3 bits is used can be accommodated. Therefore, it is preferable thatthe Alt-1 scheme is applied to PUCCH Report Mode 1-1-2.

Hereinafter, the subsampling scheme capable of being applied to PUCCHReport Mode 2-1 will be described in detail.

In PUCCH Report Mode 2-1, four report types [(RI+PTI), (W1)_WB,(W2+CQI)_WB, (W2+CQI)_SB)] may be fed back. Each report type may bechanged according to PTI selection. Table 45 shows signaling overheadrequired for each report type in case of PUCCH Mode 2-1 (denoted byMode-C in Table 45). It is assumed that, in case of the (W2+CQI)_SBreporting at PTI=1, an L-bit indicator for a UE-selected subband iscontained in Table 45.

In Table 45, in case of Rank-2, Rank-3, and Rank-4 on the condition thatPTI=1 is indicated, overhead required for reporting the L-bit indicatorfor each of (W2+CQI)_SB and SB exceeds 11 bits. Associated signalingoverhead must be reduced such that PUCCH Format 2 of 3GPP LTE Release-8can be reused. In order to reduce signaling overhead, the following twomethods (Option 1 and Option 2) can be used. Option 1 can newly define apredetermined SB cycling without using the selected band indicator of Lbits. Option 2 performs W2 subsampling such that the L-bit selected bandindicator can be reused.

In case of Option 1, SB CQI and SB W2 may be reported through PUCCHFormat 2. However, according to Option 1, a CQI report cycle for eachsubband is increased, such that performance deterioration can be moresensitively generated at a time-selective channel using the predefinedSB period. In addition, WB CQI and WB W2 should be reported between theperiods of the BP (Bandwidth Part) report duration, such that the CQIreport cycle at each subband can be considerably increased, resulting inincreased performance deterioration.

In case of Option 2, SB CQI and SB W2 are reported along with the L-bitselected bandwidth indicator, such that the number of bits required forperforming such reporting at Rank-2, Rank-3, and Rank-4 exceeds aspecific value of 11. Therefore, W2 subsampling can be applied, andTable 55 shows the example of W2 subsampling.

TABLE 55 Alternative W2 Rank-1 2 bit: (0, 1, 2, 3) Rank-2 2 bit: (0, 1,8, 9) Rank-3 2 bit: (0, 2, 8, 10) Rank-4 2 bit: (0, 1, 4, 5) Rank-5~8 0bit

Table 56 shows, in 8×2 SU-MIMO transmission, the level of systemperformance of PUCCH Report Mode 2-1 for use in Option 1 and Option 2.Table 56 shows, in case of two methods (Option 1 and Option 2), anaverage spectral efficiency (SE) and a cell-edge SE for across-polarized antenna structure and a co-polarized antenna structure.It is assumed that, in order to measure system performance, SB CQI andSB W2 are reported at every report cycle of 5 ms, and WB W1 is updatedat intervals of 45 ms. In addition, it is assumed that 2-bit subsampledW2 is applied to Option 2.

TABLE 56 Cross-polarized (4 λ) Co-polarized (0.5 λ) Antenna AntennaAverage Cell Average Cell Feedback information SE Edge SE SE Edge SE(W1 + W2 for rank-1) (bps/Hz) (bps/Hz) (bps/Hz) (bps/Hz) Option-1: 1.630.0472 2.24 0.0892 Predefined cycling (0.00%) (0.00%) (0.00%) (0.00%)(4 + 4) Option-2: 1.70 0.0480 2.30 0.0896 UE band selection (4.00%)(1.00%) (3.00%) (0.00%) with W2 subsampling (4 + 2)

As can be seen from Table 56, the average SE of Option 1 is lower thanthat of Option 2 by a system performance deterioration of 3% to 4%,because the report operation period of WB CQI/WB W2 for Option 1 islonger than that of Option 2. For example, in the same manner as in FIG.33 illustrating reporting periods in case that the predefined SB cyclingat the system bandwidth of 5 MHz, Option 1 reports CSIs of all subbands,such that the report cycle of WB CQI/WB W2 is longer than that of Option2.

As described above, Option 2 has higher performance than Option 1, suchthat an L-bit indicator for a UE-selected band is preferably includedand W2 subsampling is applied to Option 2 in terms of systemperformance. In addition, the UE band selection function has alreadybeen used in the legacy system (3GPP LTE Release-8 system), such thatcomplexity for Option 2 implementation is also reduced.

Therefore, according to the inventive codebook subsampling schemeapplied to each PUCCH mode, the legacy PUCCH format 2 is reused andsystem performance deterioration can be minimized.

On the other hand, Table 57 shows parameters applied to simulation ofsystem performances shown in Tables 52, 54, and 56. In addition, Tables58, 59 and 60 show parameters applied to simulations of systemperformances of PUCCH Format 1-1-1, PUCCH Format 1-1-2, and PUCCH Format2-1.

TABLE 57 Parameter Assumption Number of cells 57 Deployment model Hexgrid, 3 sector sites Inter site distance 200 m Average number of UEs percell 10 Traffic model Full buffer UE speeds of interest 3 km/h Bandwidth5 MHz Carrier frequency 2.5 GHz Control OFDM symbols  3 per RB pair Maxnumber of HARQ  5 retransmissions Channel model ITU Urban Micro BSantenna configuration Two closely spaced ±45° cross-poles with 0.5 λseparation ULA with 0.5 λ separation and vertical polarization UEantenna configuration 2 Rx: cross-polarized 0°/90°, 0.5 λ separationReceiver MMSE with no inter-cell interference suppression SchedulerProportional fair in time and frequency Channel estimation Perfectchannel estimation Outer-loop link adaptation Yes Target BLER 10% Numberof RBs per subband 4 RBs Number of Subband  8 Number of Bandwidth part 2 Frequency granularity for CQI 4 RBs reporting Feedback delay 5 msFeedback codebook for 8Tx LTE-A 8Tx codebook transmission

TABLE 58 RI reporting periodicity 20 ms CQI reportingperiodicity/frequency  5 ms/Wideband granularity PMI reporting W1 20ms/Wideband periodicity/frequency granularity PMI reporting W2  5ms/Wideband periodicity/frequency granularity Transmission mode SU-MIMO(Rank adaptation - up to Rank-2)

TABLE 59 RI reporting periodicity 20 ms CQI reportingperiodicity/frequency  5 ms/Wideband granularity PMI reporting W1  5ms/Wideband periodicity/frequency granularity PMI reporting W2  5ms/Wideband periodicity/frequency granularity Transmission mode SU-MIMO(Rank adaptation - up to Rank-2)

TABLE 60 RI reporting periodicity 45 ms CQI reportingperiodicity/frequency  5 ms/Wideband granularity PMI reporting W1 45ms/Wideband periodicity/frequency granularity PMI reporting W2  5ms/Subband periodicity/frequency granularity Transmission mode MU-MIMO(Rank-1 per UE, Max 2-Layer pairing) ZF beamforming Codebook subsamplingFor UE band selection, all codebook for W1 and subsampling for W2: 2 bit(0, 1, 2, 3)

Embodiment 11-B

In MU-MIMO transmission, the number of transmission (Tx) layers of atransmitter is different from the number of reception (Rx) layers of areceiver. In addition, the receiver reports CSI on the assumption ofSU-MIMO, such that channel information reported by the receiver may bedifferent from actual channel information (That is, the channelinformation reported by the receiver may be mismatched with the actualchannel information). For example, in the case of using the legacy PUSCHreport mode 3-1, CSI of MU-MIMO is incorrectly fed back, such that thereis needed a method for improving the CQI reporting.

As one solution for obviating the above-mentioned problem, a method foradditionally reporting MU-MIMO CQI may be considered in the legacy PUSCHreport mode 3-1. Therefore, flexible scheduling between SU-MIMO andMU-MIMO modes is allowed to optimize system performance. However, inorder to support dynamic switching between SU-MIMO and MU-MIMO modes,MU-MIMO CQI must be attached to SU-MIMO CQI and the attached result mustbe fed back so that additional overhead for MU-MIMO CQI feedback isneeded.

As another solution, a new PUSCH report mode may be used. For example,PUSCH report mode 3-2 may be used in which WB CQI for a first codeword(CW), and WB CQI, WB W1 and SB W2 for a second CW are transmitted. ByPUSCH report mode 3-2, a PMI for more precise frequency granularity maybe fed back so that accuracy of feedback information can be improved.Although additional MU-MIMO CQI feedback is not required for PUSCHreport mode 3-2, feedback overhead is increased to improve more precisePMI feedback frequency granularity.

The following Table 61 illustrates, in 4Tx antenna transmission,feedback overhead required for PUSCH report mode 3-1, feedback overheadrequired for PUSCH report mode 3-1 and additional MU-MIMO CSI, andfeedback overhead required for PUSCH report mode 3-2. In Table 61, N isthe number of subbands (SBs), and L is the number of bits required forindicating the selected band.

TABLE 61 Feedback information Rank-1 Rank-2~4 PUSCH reporting mode CQI:4 + 2 × N CQI: (4 + 2 × N) × 2 3-1 PMI: 4 PMI: 4 22, 26, 34 40, 48, 64(5, 10, 20 MHz) PUSCH reporting mode CQI: (4 + 2 × N) × 2 CQI: (4 + 2 ×N) × 3 3-1 with additional PMI: 4 PMI: 4 × 2 MU-MIMO CQI 40, 48, 64 62,74, 98 PUSCH reporting mode CQI: 4 + 2 × N CQI: (4 + 2 × N) × 2 3-2 PMI:4 × N PMI: 4 × N 46, 58, 82 64, 80, 112

As can be seen from Table 61, feedback overhead for use in two CQIreport improvement methods (both a MU-MIMO CQI transmission method and amethod for using PUSCH report mode 3-2) is larger than that of the PUSCHreport mode 3-1. feedback overhead. Therefore, in order to apply theabove-mentioned CQI report improvement schemes, a sufficient performancegain is needed.

Tables 62 to 64 illustrate system level performances for individual CQIimprovement methods in 4×2 MU-MIMO transmission. In Tables 62 to 64, itis assumed that only one layer is assigned to one UE. In Tables 62 and63, a maximum number of MU-MIMO scheduled UEs is set to 2. In Table 64,a maximum number of MU-MIMO scheduled UEs is set to 4. For MU-MIMO CQIcalculation, it is assumed that the UE searches for a preferred beamvector in a similar way to the SU-MIMO scheme and other interferencebeam vectors are predefined. Therefore, a precoder is formed by onepreferred beam vector and other interference beam vectors inconsideration of co-channel interference, and MU-MIMO CQI calculationcan be performed on the basis of the formed precoder.

TABLE 62 Cross-polarized (4 λ) Co-polarized (0.5 λ) Antenna AntennaAverage Cell Feedback SE Cell Edge SE Average SE Edge SE information(bps/Hz) (bps/Hz) (bps/Hz) (bps/Hz) PUSCH mode 3-1 1.70 0.0560 2.220.0911 (0.00%) (0.00%) (0.00%) (0.00%) PUSCH mode 3-1 1.70 0.0559 2.230.0910 with additional (0.00%) (0.00%) (0.00%) (0.00%) MU-MIMO CQI PUSCHmode 3-2 1.74 0.0568 2.23 0.0930 (2.00%) (1.00%) (0.00%) (1.00%)

TABLE 63 Cross-polarized (4 λ) Co-polarized (0.5 λ) Antenna AntennaAverage Cell Feedback SE Cell Edge SE Average SE Edge SE information(bps/Hz) (bps/Hz) (bps/Hz) (bps/Hz) PUSCH mode 3-1 1.73 0.0550 2.230.0882 (0.00%)   (0.00%) (0.00%) (0.00%) PUSCH mode 3-1 1.71 0.0540 2.210.0880 with additional (−1.10%)   (−1.70%) (−1.00%)   (−0.20%)   MU-MIMOCQI PUSCH mode 3-2 1.75 0.0544 2.23 0.0904 (1.10%) (−1.00%) (0.00%)(2.30%)

TABLE 64 Cross-polarized (4 λ) Co-polarized (0.5 λ) Antenna AntennaAverage Cell Feedback SE Cell Edge SE Average SE Edge SE information(bps/Hz) (bps/Hz) (bps/Hz) (bps/Hz) PUSCH mode 3-1 1.73 0.0560 2.340.0922 (0.00%) (0.00%)   (0.00%)   (0.00%) PUSCH mode 3-1 1.82 0.05402.32 0.0918 with additional (5.20%) (−3.50%)   (−0.85%) (−0.69%) MU-MIMOCQI PUSCH mode 3-2 1.79 0.0564 2.33 0.0921 (3.40%) (1.00%) (−0.43%)(−0.20%)

As can be seen from In Tables 62 to 64, the above-mentioned CQIimprovement methods can obtain higher performance gain than theconventional PUSCH report mode 3-1. If necessary, a performance gaincapable of being obtained by the CQI improvement method is not high, amethod for using the conventional PUSCH report mode 3-1 may also be usedinstead of using the CQI improvement method increasing signalingoverhead.

Table 65 shows the number of bits required for indicating the number ofsubbands (SBs) and the number of bits required for subband indication.

TABLE 65 5 MHz 10 MHz 20 MHz (25 RBs) (50 RBs) (100 RBs) Mode Subbandsize 4 RBs 6 RBs 8 RBs 3-1/ The number of 7 9 13 3-2 subbands (N)

Table 66 illustrates parameters applied to simulation of systemperformances of Tables 62 to 64.

TABLE 66 Parameter Assumption Number of cells 57 Deployment model Hexgrid, 3 sector sites Average number of UEs per cell 10 Traffic modelFull buffer Bandwidth 10 MHz Channel model ITU Urban Micro Antennaconfiguration 4Tx-2Rx BS antenna configuration ULA with 0.5 λ separationand vertical polarization Two closely spaced ±45° cross-poles with 4λseparation UE antenna configuration ULA with, 0.5 λ separationCross-polarized 0°/90°, 0.5 λ separation Receiver MMSE with nointer-cell interference suppression Scheduler Proportional fair in timeand frequency Channel estimation Perfect channel estimation Outer-looplink adaptation Yes Target BLER 10% Max number of HARQ  5retransmissions PUSCH Number of RBs per 6 RBs Feedback subband Mode 3-1CQI reporting 5 ms/Subband periodicity/frequency granularity PMIreporting 5 ms/Wideband periodicity/frequency granularity PUSCH Numberof RBs per 6 RBs Feedback subband Mode 3-2 CQI reporting 5 ms/Subbandperiodicity/frequency granularity PMI reporting 5 ms/Subbandperiodicity/frequency granularity Feedback delay 5 ms RI reportingperiodicity 20 ms Feedback codebook Release-8 HH Transmission modeMU-MIMO: ZF beamforming, Rank-1 per UE, Max 2 Layer pairing CQIreporting type SU-MIMO based CQI MU-MIMO based CQI [4] Overhead PDCCH 3OFDM symbols CRS 2-Tx pattern DMRS 12 REs per RB for rank-1 and 2

A method for transmitting channel status information according to anembodiment of the present invention will hereinafter be described withreference to FIG. 34.

In association with DL transmission from a BS (or eNB) to a UE, the UEmeasures a DL channel state and feeds back the measured result throughuplink. For example, if 8 Tx antennas are applied to DL transmission ofthe BS, the BS can transmit CSI-RS (Channel status information—ReferenceSignal) through 8 antenna ports (Antenna port indexes 15 to 22). The UEmay transmit the DL channel state measurement results (RI, PMI, CQI,etc.) through the CSI-RS. The above-mentioned various examples of thepresent invention can be applied to a detailed method forselecting/calculating RI/PMI/CQI. The BS may determine the number of DLtransmission layers, the precoder, and MCS (Modulation Coding Scheme)level, etc. according to the received channel status information(RI/PMI/CQI), such that it can transmit a DL signal.

In step S3410 of FIG. 34, the base station may transmit a downlinksignal through a downlink channel, and the UE may receive the same.

In step S3420, the UE may generate channel statin information (CSI) forthe downlink channel. The generated CSI may include at least one of RI,PMI and CQI.

Here, the generated CSI may include a first type CSI determined based ona rank N determined by the UE and/or a second type CSI determined basedon a rank restricted by a reference value M. For example, in case ofN>M, both of the first type CSI and the second type CSI are generated.Alternatively, in case of N≦M, only the first type CSI is generated.

In addition, the PMI included in the second type CSI may be configuredas a subset of the PMI included in the first type CSI.

The feedback mode (WB or SB) of the second type CSI may be determinedbased on the feedback mode (WB or SB) of the first type CSI, or may beindependently determined regardless of the first type CSI.

In step S3430, the UE may transmit the generated CSI (the first type CSIand/or the second type CSI) through an uplink channel (PUCCH or PUSCH).

In addition, at least the RI, the PMI and the CQI of the first type CSI,and the CQI of the second type CSI may be transmitted, and the PMI ofthe second type CSI or a precoder selection indicator (PSI) may beadditionally transmitted.

In case where the CSI is transmitted through PUSCH, that is, aperiodicCSI reporting, the first type CSI or the second type CSI may betransmitted based on the DCI (DCI format 0 or 4) including CSI reportrequest field. For example, the first type CSI may be transmitted if theDCI format includes information on uplink multiple transport blocksscheduling. The second type CSI may be transmitted, if the DCI formatincludes information of a single transport block scheduling or includesinformation on the reference value M. Further, the first type CSI or thesecond type CSI may be transmitted according to whether an index of adownlink subframe in which the DCI format PDCCH is received is an evennumber (2k, wherein k is a natural number) or an odd number (2k+1).Further, the first type CSI or the second type CSI may be transmittedaccording to whether an index of an uplink subframe in which the CSI istransmitted is an even number (2k) or an odd number (2k+1).

In case where the CSI is transmitted through PUCCH, that is, periodicCSI reporting, the second type CSI may be transmitted in a part ofuplink subframes configured for transmitting the first type CSI.Further, the second type CSI may be transmitted in an uplink subframewhich is after, by a predetermined offset, an uplink subframe in whichthe first type CSI is transmitted.

The PMI may include a first index (W1 or I1) and a second index (W2 orI1), the CQI may be determined based on a combination of the first andthe second index.

In accordance with the CSI transmission method shown in FIG. 34, eachitem disclosed in various embodiments of the present invention may beindependently applied or two or more embodiments may be simultaneouslyapplied. The same parts may herein be omitted for convenience andclarity of description.

The same principles proposed by the present invention can be applied notonly to CSI feedback for one MIMO transmission between a base station(BS) and a relay node (RN) (i.e., MIMO transmission between backhauluplink and backhaul downlink) but also to CSI feedback for MIMOtransmission between an RN and a UE (i.e., MIMO transmission between anaccess uplink and an access downlink).

FIG. 35 is a block diagram illustrating an eNB apparatus and a userequipment (UE) apparatus according to an embodiment of the presentinvention.

Referring to FIG. 35, an eNB apparatus 3510 may include a reception (Rx)module 3511, a transmission (Tx) module 3512, a processor 3513, a memory3514, and a plurality of antennas 3515. The plurality of antennas 3515may be contained in the eNB apparatus supporting MIMO transmission andreception. The reception (Rx) module 3511 may receive a variety ofsignals, data and information in uplink starting from the UE. Thetransmission (Tx) module 3512 may transmit a variety of signals, dataand information in downlink for the UE. The processor 3513 may provideoverall control to the eNB apparatus 3510.

The eNB apparatus 3510 according to one embodiment of the presentinvention may be configured to transmit DL transmission through amaximum of 8 Tx antennas as well as to receive CSI of the DLtransmission from the UE apparatus 3520. The processor 3513 of the eNBapparatus may be configured to transmit, using the Tx module 3512, adownlink signal through a downlink channel. Further, the processor 3513may be configured to receive, using the Rx module 3511, the CSI throughan uplink channel, wherein the CSI includes at least one of RI, PMI, andCQI, for the downlink channel. Here, the CSI includes at least one of afirst type CSI that is determined based on rank N determined by the UEand a second type CSI that is determined based on a rank restricted by areference value M.

Besides, the processor 3513 of the eNB apparatus 3510 processesinformation received at the eNB apparatus 3510 and transmissioninformation. The memory 3514 may store the processed information for apredetermined time. The memory 3514 may be replaced with a componentsuch as a buffer (not shown).

Referring to FIG. 35, the UE apparatus 3520 may include a reception (Rx)module 3521, a transmission (Tx) module 3522, a processor 3523, a memory3524, and a plurality of antennas 3525. The plurality of antennas 3525may be contained in the UE apparatus supporting MIMO transmission andreception. The reception (Rx) module 3521 may receive a variety ofsignals, data and information on downlink starting from the eNB. Thetransmission (Tx) module 3522 may transmit a variety of signals, dataand information on uplink for the eNB. The processor 3523 may provideoverall control to the UE apparatus 3520.

The UE apparatus 3520 according to one embodiment of the presentinvention may be configured to receive DL transmission through a maximumof 8 Tx antennas as well as to feed back CSI of the DL transmission tothe eNB apparatus 3510. The processor 3523 of the UE apparatus 3520 maybe configured to receive, using the Rx module 3521, a downlink signalthrough a downlink channel. Further, the processor 3523 may beconfigured to generate the CSI including at least one of RI, PMI, andCQI, for the downlink channel. Further, the processor 3523 may beconfigured to transmit, using the Tx module 3522, the CSI through anuplink channel. Here, the CSI includes at least one of a first type CSIthat is determined based on rank N determined by the UE and a secondtype CSI that is determined based on a rank restricted by a referencevalue M.

Besides, the processor 3523 of the UE apparatus 3520 processesinformation received at the UE apparatus 3520 and transmissioninformation. The memory 3524 may store the processed information for apredetermined time. The memory 3524 may be replaced with a componentsuch as a buffer (not shown).

In association with the above-mentioned eNB and UE apparatuses, thecontents described in the above-mentioned embodiments may be usedindependently of each other or two or more embodiments may besimultaneously applied, and the same parts may herein be omitted forconvenience and clarity of description.

The eNB apparatus 3510 shown in FIG. 35 may also be applied to a relaynode (RN) acting as a DL transmission entity or UL reception entity, andthe UE apparatus 3520 shown in FIG. 35 may also be applied to a relaynode (RN) acting as a DL reception entity or UL transmission entity.

The above-described embodiments of the present invention can beimplemented by a variety of means, for example, hardware, firmware,software, or a combination of thereof.

In the case of implementing the present invention by hardware, thepresent invention can be implemented with application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), a processor, a controller, amicrocontroller, a microprocessor, etc.

If operations or functions of the present invention are implemented byfirmware or software, the present invention can be implemented in theform of a variety of formats, for example, modules, procedures,functions, etc. Software code may be stored in a memory unit so that itcan be driven by a processor. The memory unit may be located inside oroutside of the processor, so that it can communicate with theaforementioned processor via a variety of well-known parts.

The detailed description of the exemplary embodiments of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the exemplary embodiments, those skilled in the artwill appreciate that various modifications and variations can be made inthe present invention without departing from the spirit or scope of theinvention described in the appended claims. For example, those skilledin the art may use each construction described in the above embodimentsin combination with each other. Accordingly, the invention should not belimited to the specific embodiments described herein, but should beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above exemplary embodiments are therefore to beconstrued in all aspects as illustrative and not restrictive. The scopeof the invention should be determined by the appended claims and theirlegal equivalents, not by the above description, and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein. Also, it will be obvious to thoseskilled in the art that claims that are not explicitly cited in theappended claims may be presented in combination as an exemplaryembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention are applicable to a variety ofmobile communication systems (for example, OFDMA, SC-FDMA, CDMA, andTDMA communication systems based on multiple access technology).

The invention claimed is:
 1. A method for transmitting channel state information, CSI, for a downlink transmission from a base station at a user equipment, UE, through an uplink in a wireless communication system, the method comprising: receiving a downlink signal through a downlink channel; generating the CSI including at least one of a rank indicator, RI, a precoding matrix indicator, PMI, and a channel quality indicator, CQI, for the downlink channel; and transmitting the CSI through an uplink channel, wherein the CSI includes at least one of a first type CSI that is determined based on rank N determined by the UE and a second type CSI that is determined based on a rank restricted by a reference value M, wherein if the uplink channel is a physical uplink shared channel, PUSCH, the first type CSI or the second type CSI is transmitted based on downlink control information, DCI, including a CSI report request field, and wherein the first type CSI or the second type CSI is transmitted based on whether an index of a downlink subframe in which the DCI is received or an index of an uplink subframe in which the CSI is transmitted is 2k+1 (where k is a natural number).
 2. The method according to claim 1, wherein the CSI includes the first type CSI and the second type CSI if N>M, and wherein the CSI include the first type CSI if N≦M.
 3. The method according to claim 1, wherein the first type CSI or the second type CSI is transmitted further based on whether information on scheduling uplink multiple transport blocks is included in the DCI or information on scheduling uplink single transport block is included in the DCI, or wherein the first type CSI or the second type CSI is transmitted further based on whether information on the reference value M is included in the DCI or not.
 4. The method according to claim 1, wherein the PMI included in the second type CSI is configured as a subset of the PMI included in the first type CSI, and wherein the subset is selected according to a predetermined rule, or information on a selection of the subset is included in the CSI.
 5. The method according to claim 1, wherein the transmitting the CSI includes transmitting the RI, the PMI and the CQI of the first type CSI, and the CQI of the second type CSI.
 6. The method according to claim 5, wherein the transmitting the CSI further includes transmitting the PMI of the second type CSI or a precoder selection indication, PSI.
 7. The method according to claim 1, wherein, if the uplink channel is a physical uplink control channel, PUCCH, the second type CSI is transmitted instead of the first type CSI in a part of uplink subframes configured for transmitting the first type CSI.
 8. The method according to claim 1, wherein, if the uplink channel is a physical uplink control channel, PUCCH, wherein the second type CSI is transmitted in an uplink subframe which is after, by a predetermined offset, an uplink subframe in which the first type CSI is transmitted.
 9. The method according to claim 1, wherein a downlink bandwidth represented by the second type CSI is determined based on the first type CSI.
 10. The method according to claim 1, wherein the PMI includes a first index and a second index, and wherein the CQI is determined by a combination of the first index and the second index.
 11. A method for receiving channel state information, CSI, for a downlink transmission at a base station through an uplink from a user equipment, UE, in a wireless communication system, the method comprising: transmitting a downlink signal through a downlink channel; and receiving the CSI through an uplink channel, wherein the CSI includes at least one of a rank indicator, RI, a precoding matrix indicator, PMI, and a channel quality indicator, CQI, for the downlink channel, wherein the CSI includes at least one of a first type CSI that is determined based on rank N determined by the UE and a second type CSI that is determined based on a rank restricted by a reference value M, wherein if the uplink channel is a physical uplink shared channel, PUSCH, the first type CSI or the second type CSI is transmitted based on downlink control information, DCI, including a CSI report request field, and wherein the first type CSI or the second type CSI is transmitted based on whether an index of a downlink subframe in which the DCI is received or an index of an uplink subframe in which the CSI is transmitted is 2k+1 (where k is a natural number).
 12. A user equipment, UE, for transmitting channel state information, CSI, for a downlink transmission through an uplink in a wireless communication system, the UE comprising: a receiving module configured to receive a downlink signal from a base station; a transmitting module configured to transmit an uplink signal to the base station; and a processor configured to control the UE including the receiving module and the transmitting module, wherein the processor is further configured to: receive, using the receiving module, a downlink signal through a downlink channel; generate the CSI including at least one of a rank indicator, RI, a precoding matrix indicator, PMI, and a channel quality indicator, CQI, for the downlink channel; and transmit, using the transmitting module, the CSI through an uplink channel, wherein the CSI includes at least one of a first type CSI that is determined based on rank N determined by the UE and a second type CSI that is determined based on a rank restricted by a reference value M, wherein if the uplink channel is a physical uplink shared channel, PUSCH, the first type CSI or the second type CSI is transmitted based on downlink control information, DCI, including a CSI report request field, and wherein the first type CSI or the second type CSI is transmitted based on whether an index of a downlink subframe in which the DCI is received or an index of an uplink subframe in which the CSI is transmitted is 2k+1 (where k is a natural number).
 13. A base station for receiving channel state information, CSI, for a downlink transmission through an uplink in a wireless communication system, the base station comprising: a receiving module configured to receive an uplink signal from a user equipment, UE; a transmitting module configured to transmit a downlink signal to the UE; and a processor configured to control the base station including the receiving module and the transmitting module, wherein the processor is further configured to: transmit, using the transmitting module, a downlink signal through a downlink channel; and receive, using the receiving module, the CSI through an uplink channel, wherein the CSI includes at least one of a rank indicator, RI, a precoding matrix indicator, PMI, and a channel quality indicator, CQI, for the downlink channel, wherein the CSI includes at least one of a first type CSI that is determined based on rank N determined by the UE and a second type CSI that is determined based on a rank restricted by a reference value M, wherein if the uplink channel is a physical uplink shared channel, PUSCH, the first type CSI or the second type CSI is transmitted based on downlink control information, DCI, including a CSI report request field, and wherein the first type CSI or the second type CSI is transmitted based on whether an index of a downlink subframe in which the DCI is received or an index of an uplink subframe in which the CSI is transmitted is 2k+1 (where k is a natural number). 